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CO4 Discuss and apply comprehensively the concepts, properties and theorems of functions, limits, continuity and the derivatives in determining the derivatives of algebraic functions

R lecture co4_math 21-1

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Page 1: R lecture co4_math 21-1

CO4Discuss and apply comprehensively the concepts, properties and theorems of functions, limits, continuity and the derivatives in determining the derivatives of algebraic functions

Page 2: R lecture co4_math 21-1

Objective:

At the end of the discussion, the students should be able to evaluate limits and determine the derivative of a continuous algebraic function given in the explicit or implicit form.

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The Calculus

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Calculus- Is the mathematics of change- two basic branches: differential and integral

calculus

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Lesson 1 : Functions and Limits

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FUNCTIONS

- A relation between variables x and y is a rule of correspondence that assigns an element x from the Set A to an element y of Set B.

- A function f from set A to set B is a rule of correspondence that assigns to each element x in the set A exactly one element y in the set B. It is a set of ordered pairs ( x, y) such that no two pairs will have the same first element.

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Domain (set of all x’s) Range (set of all y’s)

1

2

3

4

5

2

10

8

6

4

Mapping of X- values into y-values ( 1 -1 correspendence)

X Y

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X = Set A

Domain Set

1

2

3

4

5

Y = Set B

Range Set

2

1086

4

Mapping illustrating many – 1 correspondence

Page 9: R lecture co4_math 21-1

1

2

3

4

5

2

1086

4

Mapping of the elements of Set A in to Set B illustrating 1 – many type of correspondence.

X = Set A Y = Set B

Page 10: R lecture co4_math 21-1

Function Notation

We commonly name a function by letter with f the most commonly used letter to refer to functions. However, a function can be referred to by any letter.

The function called f

The independent variable, x

f(x) defines a rule express in terms of x as given by the right

hand side expression.

Note: The value of the function f(x) is determined by substituting x- value into the expression.

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PIECEWISE DEFINED FUNCTION

A piecewise defined function is function defined by different formulas on different parts of its domain; as in,

Page 12: R lecture co4_math 21-1

Graph of a Function

The graph of a function f consists of all points (x, y) whose coordinates satisfy y = f(x), for all x in the domain of f. The set of ordered pairs (x, y) may also be represented by (x, f(x)) since y = f(x).

Recall: The Vertical Line Test

A set of points in a coordinate plane is the graph of a function y = f(x) if and only if no vertical line intersects the graph at more than one point.

Page 13: R lecture co4_math 21-1

ODD and EVEN FUNCTIONS

A function is an even function if and only if The graph of an even function is symmetric with respect to the y-axis.

A function is an odd function if and only if The graph of an odd function is symmetric with respect to the origin.

Page 14: R lecture co4_math 21-1

Sample Problems

For each of the following, determine the domain and range, then sketch the graph.

1x if 1x21x if x

)x(f d.

3xx2)x(f g. x)x(f .c

1x3x)x(f .f x1)x(f .b

4t4t4

4t

ififif

t1t

3)t(f e. 5x3)x(f .a

2

2

Page 15: R lecture co4_math 21-1

with domain the set of all x in the domain of g such that g(x) is in the domain of f or in other words, whenever both g(x) and f(g(x)) are defined.

In the same way,

with domain as the set of all x in the domain of f such that f(x) is in the domain of g, or, in other words, whenever both f(x) and g(f(x)) are defined.

The composition function, denoted by , is defined as

Page 16: R lecture co4_math 21-1

For each of the following pair of functions:

a) f(x) = 2x – 5 and g(x) = x2 – 1

b) and

determine the following functions: a) f + g b) f - g c) fg d) f/g e) g/f

f) g) domain of each resulting functions.

Sample Problems

Page 17: R lecture co4_math 21-1

Limits

Informal Definition: If the values of f(x) can be made as close as possible to some value L by taking the value of x as close as possible, but not equal to, a, then we write

Read as “ the limit of f(x) as x approaches a is L” or “ f(x) approaches L as x approaches a”. This can also be written as

Page 18: R lecture co4_math 21-1

Formal Definition of a Limit of a Function:

Let f be a function defined at every number in some open interval containing a , except possibly at the number a itself. The limit of f(x) as x approaches a is L , written as,

If given any

Page 19: R lecture co4_math 21-1

Geometrically, this can be viewed as follows:

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Theorem 1: Limit of a Constant If c is a constant, then for any number a

Theorem 2: Limit of the Identify Function Theorem 3: Limit of a Linear Function

If m and b are constants

Theorem 4: Limit of the Sum or Difference of Functions

Theorems on Limits

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Theorem 5: Limit of the Product

Theorem 6: Limit of the nth Power of a function

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Theorem 7: Limit of a Quotient

Theorem 8: Limit of the nth Root of a Function

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Using the theorems on Limits, evaluate each of the following:

1. 6. Let

2. find:

3.

4.

5.

Sample Problems

)t(glim ),t(glim2t0t

Page 24: R lecture co4_math 21-1

Definition of One-Sided LimitsInformal Definition:If the value of f(x) can be made as close to L by taking the value of x sufficiently close to a , but always greater than a , then

read as “the limit of f(x) as x approaches a from the right is L.”Similarly, if the value of f(x) can be made as close to L by taking the value of x sufficiently close to a , but always less than a , then

read as “the limit of f(x) as x approaches a from the left is L.”If both statements are true and equal then .

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Geometrically,

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Infinite Limits

The expressions

denote that the function increases/decreases without bound as x approaches a from the right/ left and that f(x) has infinite limit.

A function having infinite limit at a exhibits a vertical asymptote at x = a.

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Page 30: R lecture co4_math 21-1

x=a

0

x=a

0

Geometrically;

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Limits at Infinity

If as x increases/decreases without bound, the value of the function f(x) gets closer and closer to L then

If L is finite, then limits at infinity is associated with the existence of a horizontal asymptote at y = L.

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Geometrically,

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Y=L

0

Y=L0

Page 34: R lecture co4_math 21-1

LIMITS OF FUNCTIONS USING THE SQUEEZE PRINCIPLE The Squeeze Principle is used on limit problems where the usual algebraic methods (factoring, conjugation, algebraic manipulation, etc.) are not effective. However, it requires that you be able to ``squeeze'' your function in between two other ``simpler'' functions whose limits are easily evaluated and equal. The use of the Squeeze Principle requires accurate analysis, deft algebra skills, and careful use of inequalities.

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Theorem:

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Sample Problems

3xxcos2lim .2

x

2xxlim .9

x)xcos1(xsinlim .8

x31

x31

lim .7

4x35xlim .6

2x

20x

0x

4x

Page 37: R lecture co4_math 21-1

Sample Problems

x

- x

23

x

3

23

x

0x

e52lim .141x4

x5lim .13

2x4x9x4x2x7lim .12

x2cos1x4cos1lim .11

Page 38: R lecture co4_math 21-1

Lesson 2 : Continuity of Function

Page 39: R lecture co4_math 21-1

If one or more of the above conditions fails to hold at c the function is said to be discontinuous at c. A function that is continuous on the entire real line is said to be continuous everywhere.

DEFINITION: CONTINUITY OF A FUNCTION

Definition:A function f(x) is said to be conrinuous at x = c if

and only if the following conditions hold:

Page 40: R lecture co4_math 21-1

If functions f and g are continuous functions at x = c, then the following are true:

a. f + g is continuous at cb. f – g is continuous at cc. fg is continuous at cd. f/g is continuous at c provided g( c ) is not zero.

Page 41: R lecture co4_math 21-1

The figure above illustrates that the function is discontinuous at x=c and violates the first condition.

The figure above illustrates that the function is discontinuous at x = c and violates the second condition. This kind of discontinuity is called jump discontinuity.

Types of Discontinuity

Page 42: R lecture co4_math 21-1

The figure above illustrates that the limit coming from the right and left of c are both undefined, thus the function is discontinuous at x = c and violates the second condition. This kind of discontinuity is called infinite discontinuity.

The figure above shows that the function is defined at c and that the limit coming from the right and left of c both exist thus the two sided limit exist. However,Thus, the function is discontinuous at x = c, violating the third condition. This kind of discontinuity is calledremovable discontinuity ( missing point).

Page 43: R lecture co4_math 21-1

1. Investigate the discontinuity of the function f defined. What type of discontinuity is illustrated?

a)

b)

Show the point(s) of discontinuity by sketching the graph of the function .

Sample Problems

Page 44: R lecture co4_math 21-1

2. Find values of the constants k and m, if possible, that will make the function f(x) defined as

be continuous everywhere.

1x2x1

2x

7xx2k)1x(m

5x)x(f

3

2

Page 45: R lecture co4_math 21-1

Lesson 3: The Derivative

Page 46: R lecture co4_math 21-1

Derivative of a Function

The process of finding the derivative of a function is called differentiation and the branch of calculus that deals with this process is called differential calculus. Differentiation is an important mathematical tool in physics, mechanics, economics and many other disciplines that involve change and motion.

Page 47: R lecture co4_math 21-1

y

))(,( 11 xfxP ))(,( 22 xfxQ

)(xfy

xxxxxx

12

12

tangent line

secant line

x

y

Consider:-Two distinct points P and Q-Determine slope of the secant line PQ- Investigate how the slope changes as Q approaches P.- Determine the limit of the secant line as Q approaches P.

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DEFINITION:Suppose that is in the domain of the function f, the tangent line to the curve at the point is with equation

1x)(xfy ))(,( 11 xfxP

)()( 11 xxmxfy

where provided the limit exists, and

is the point of tangency.

))(,( 11 xfxP

xxfxxfm

x

)()(lim 110

Page 49: R lecture co4_math 21-1

DEFINITION

The derivative of at point P on the curve is equal to the slope of the tangent line at P, thus the derivative of the function f with respect to x, given by , at any x in its domain is defined as:

)(xfy

0 0

( ) ( )lim limx x

dy y f x x f xdx x x

provided the limit exists.

)(' xfdxdy

Note: A function is said to be differentiable at if the derivative of y wrt x is defined at .

0x0x

Page 50: R lecture co4_math 21-1

Other notations for the derivative of a function:

)(),(',','),(, xfdxdandxffyxfDyD xx

Note: To find the slope of the tangent line to the curve at point P means that we are to find the value of the derivative at that point P.

Page 51: R lecture co4_math 21-1

THE Derivative of a Function based on the Definition ( The four-step or increment method)

To determine the derivative of a function based on the definition (increment method or more commonly known as the four-step rule) , the procedure is as follows:

xx

yy STEP 1: Substitute for x and for y in )(xfy

STEP 2: Subtract y = f(x) from the result of step 1 to obtain in terms of x and y .x

STEP 3: Divide both sides of step 2 by .x

STEP 4: Find the limit of the expression resulting from step 3 as approaches 0.

x

Page 52: R lecture co4_math 21-1

Sample Problems

Find the derivative of each of the following functions based on the definition:

Page 53: R lecture co4_math 21-1

DERIVATIVE USING FORMULA

Finding the derivative of a function using the definition or the increment-method (four-step rule) can be laborious and tedious specially when the functions to be differentiated are complex. The theorems on differentiation will enable us to calculate derivatives more efficiently and hopefully will make calculus easy and enjoyable.

Page 54: R lecture co4_math 21-1

DIFFERENTIATION FORMULA

1. Derivative of a ConstantTheorem: The derivative of a constant function

is 0; that is, if c is any real number, then .

0][ cdxd

2. Derivative of a Constant Times a FunctionTheorem: ( Constant Multiple Rule) If f is a differentiable function at x and c is any real number, then is also differentiable at x and

)()( xf

dxdcxcf

dxd

cf

3. Derivatives of Power FunctionsTheorem: ( Power Rule) If n is a positive integer, then .

1][ nn nxxdxd

Page 55: R lecture co4_math 21-1

DIFFERENTIATION FORMULA

4. Derivatives of Sums or Differences Theorem: ( Sum or Difference Rule) If f and g are both differentiable functions at x, then so are f+g and f-g , and or

gdxdf

dxdgf

dxd

)()()()( xg

dxdxf

dxdxgxf

dxd

5. Derivative of a ProductTheorem: (The Product Rule) If f and g are both differentiable functions at x, then so is the product , and

or

gf

dxdfg

dxdgfgf

dxd

)()()]([)()()( xfdxdxgxg

dxdxfxgxf

dxd

Page 56: R lecture co4_math 21-1

DIFFERENTIATION FORMULA6. Derivative of a QuotientTheorem: (The Quotient Rule) If f and g are both differentiable functions at x, and if then is differentiable at x and

or 2gdxdgf

dxdfg

gf

dxd

0ggf

2)(

)()()()(

)()(

xg

xgdxdxfxf

dxdxg

xgxf

dxd

7. Derivatives of Composition ( Chain Rule)Theorem: (The Chain Rule) If g is differentiable at x and if f is differentiable at g(x) , then the composition is differentiable at x. Moreover, if y=f(g(x)) and u = g(x) then y = f(u) and  

gf

Page 57: R lecture co4_math 21-1

DIFFERENTIATION FORMULA

9. Derivative of a Radical with index equal to 2

If u is a differentiable function of x, then u

dxdu

udxd

2

10. Derivative of a Radical with index other than 2If n is any positive integer and u is a differentiable function of x, then  dx

duun

udxd nn

111 1

8. Derivative of a PowerIf u is a differentiable function of x and n is any real number , then

Page 58: R lecture co4_math 21-1

Implicit Differentiation

On occasions that a function F(x , y) = 0 can not be defined in the explicit form y = f(x) then the implicit form F ( x , y) = 0 can be used as basis in defining the derivative of y ( the dependent variable) with respect to x ( the independent variable).

When differentiating F( x, y) = 0, consider that y is defined implicitly in terms of x , then apply the chain rule. As a rule,1. Differentiate both sides of the equation with respect to x.2. Collect all terms involving dy/dx on the left side of the

equation and the rest of the terms on the other side.3. Factor dy/dx out of the left member of the equation and solve

for dy/dx by dividing the equation by the coefficient of dy/dx.

Page 59: R lecture co4_math 21-1

Higher Order DerivativeThe notation dy/dx represent the first derivative of y with respect to x. And if dy/dx is differentiable, then the derivative of dy/dx with respect to x gives the second order derivative of y with respect to x and is denoted by .

Given:

Page 60: R lecture co4_math 21-1

Sample Problems

Differentiate y with respect to x. Express dy/dx in simplest form.

Page 61: R lecture co4_math 21-1

Sample Problems

Determine the derivative required:

Page 62: R lecture co4_math 21-1

DIFFERENTIATION OF LOGARITHMIC

FUNCTIONS

Page 63: R lecture co4_math 21-1

TRANSCENDENTAL FUNCTIONS

Kinds of transcendental functions:1. logarithmic and exponential functions2. trigonometric and inverse trigonometric

functions3. hyperbolic and inverse hyperbolic functions

Note:Each pair of functions above is an inverse to each other.

Page 64: R lecture co4_math 21-1

A logarithmic function with the base a, a>0 and a1 is defined by

The LOGARITHMIC FUNCTIONS

ya ax ifonly and if xlogy

y

a

a x

logy form

formlExponentia

xcLogarithmi

Logarithmic Form Exponential Form

214log16 2

1

164

38log2 328

EXAMPLE:

Page 65: R lecture co4_math 21-1

SOME LOGARITHMS OF KNOWN BASES:

NATURAL LOGARITHMSLogarithms to the base e = 2.718 are called natural logarithms (from the Latin word Logarithmic Naturalis or Napieran logarithms).

COMMON LOGARITHMSLogarithms to the base 10 are called common logarithms.

xlnxlog e

xlogxlog 10

Page 66: R lecture co4_math 21-1

CHANGE OF BASEWhen the base of a logarithm is other than e or 10, express its equivalent using the base e or 10 in the formula

blnxln

blogxlogxlog or

blogxlogxlog

e

eb

a

ab

3 lny ln

3logylogylog or

3logylogylog .2

2 lnx ln

2logxlogxlog or

2logxlogxlog .1

:Example

e

e3

10

103

e

e2

10

102

Page 67: R lecture co4_math 21-1

yx then ,ylogxlog If .8 palog .7 1alog .6

01log .5 Nlogp1NlogNlog .4

NlogpNlog .3

logarithms 2 of quotient a not NlogMlog

NMlog:Note

NlogMlogNMlog .2

vedistributi not NlogMlogNMlog :Note NlogMlogMNlog 1.

1a and p,,N,M numbers positive For

aa

paa

aap1

ap

a

ap

a

a

aa

aaa

aaa

aaa

Page 68: R lecture co4_math 21-1

DIFFERENTIATION FORMULA

Derivative of Logarithmic Function The derivative of the logarithmic function for any given base and any differentiable function of u

f(x)u where; dxdu

u1)u (ln

dxd

u lnulog and 1elog but dxdu elog

u1)u(log

dxd

f(x)u where; dxdu elog

u1)u(log

dxd

eeee

aa

:e base For

:abase given any For

Page 69: R lecture co4_math 21-1

1x4lny .1

3x21ln)x(f .2

x531x3lnxf .3 2

x3

xlnxh .44

x4xlnlnxG .5

2

3

2

xln1x4lnxg .6

xlnxlny .7 2

22 x1x1xlnxxF .8

A. Find the derivative of each of the following natural logarithmic functions and simplify the result:

Page 70: R lecture co4_math 21-1

Answers on A :

1x44'y .1

12x

6xf' or x21

6x'f .2

x531x35x9x30x'f .3 2

2

x3x4

x13x'h .4

xlnxxln1x'G .5

xln1x4x31x4ln1x4xlnx8x'g .6 22

222

xlnxx1x2'y .7 2

2

2x1x lnx'F .8

Page 71: R lecture co4_math 21-1

x3logy .1 2 2

22 xlog3logxh .2

22 y3logyf .3

2x x3logxg .4

3 23 4xlogxF .5

1zz34logzH .6

2

5

1t3

3t23tlogtG .7 2

2

B. Differentiate the following logarithmic functions.

Page 72: R lecture co4_math 21-1

yx5 xy ln .1

1yx lnyx ln .2

C. Find the derivative using implicit differentiation.

Page 73: R lecture co4_math 21-1

Answers on B :elog

x1'y .1 2

elog2x1x'h .2 2

elog2y1y'f .3 2

ex

x xlog21'g .4

elog

32

4xxx'F .5 32

elog21

4z4z3z34z6z3z'H .6 523

2

elog31t33t23t

3t20t3t2t'G .7 2

23

Answers on C : y1x

1xy'y .1

xy'y . 2

Page 74: R lecture co4_math 21-1

Logarithmic Differentiation

Oftentimes, the derivatives of algebraic functions which appear complicated in form (involving products, quotients and powers) can be found quickly by taking the natural logarithms of both sides and applying the properties of logarithms before differentiation. This method is called logarithmic differentiation.

Page 75: R lecture co4_math 21-1

1. Take the natural logarithm of both sides and apply the properties of logarithms.

2. Differentiate both sides and reduce the right side to a single fraction.

3. Solve for y’ by multiplying the right side by y.4. Substitute and simplify the result.

Steps in applying logarithmic differentiation.

NOTE: Logarithmic differentiation is also applicable whenever the base and its power are both functions.

Page 76: R lecture co4_math 21-1

2x5

1x3xy if dx

dy Find .121

2

2x51x3x236x23x15

y'y

2

3

EXAMPLE:

ationdifferenti clogarithmi using

2x5ln1xln213xln

2x51x3xlnyln

:Solution

221

2

52x5

111x

121x2

3x1

y'y

2

2x51x3x2

1x3x252x53x2x51x2x2y'y

2

22

2x51x3x230x30x10x106x15x2x5x8x20x8x20

y'y

2

2323223

Page 77: R lecture co4_math 21-1

y2x51x3x2

36x23x15'y 2

3

221

3

2x51x2

36x23x15'y

2x51x3x

2x51x3x236x23x15'y

21

2

2

3

Page 78: R lecture co4_math 21-1

5 32 3x41xy if dx

dy Find .2

1x41x

x6x12x2051

1x41xx12x12x6x8

51

y'y

32

24

32

244

EXAMPLE:

ationdifferenti clogarithmi using

3x41xln513x41xlnyln

:Solution

3251

32

3x4ln1xln51yln 32

232 x12

3x41x2

1x1

51

y'y

3x41x1xx123x4x2

51

y'y

32

223

Page 79: R lecture co4_math 21-1

y

xxxxx'y

34136102

51

32

3

5132

32

3341

34136102

51

xxxx

xxx'y

151

323 3x41x3x6x10x251'y

54

323 3x41x3x6x10x52'y

Page 80: R lecture co4_math 21-1

xxy if dx

dy Find .1

xlnxylnxlnyln x

Logarithmic differentiation is also applicable whenever the base and its power are both functions. (Variable to variable power.)

Example:

1xln1x1x'y

y1

xx y butyxln1'y

xxxln1'y

Page 81: R lecture co4_math 21-1

1x2ln1xyln

1x2lnyln 1x

1x1x2y if dx

dy Find .2

11x2ln21x2

11x'yy1

1x2ln1x21x2'y

y1

1-x12x y buty1x2ln1x21x2'y

1-x12x 1x2

1x2ln1x21x2'y

1-1-x12x 1x2ln1x21x2'y

2-x12x 1x2ln1x21x2'y

Page 82: R lecture co4_math 21-1

x5x6y .3

5x6lnxyln

5x6lny lnx

x2

15x6ln5x62

65x6

1xy'y1

12x

5x6x2

5x6ln5x6x6y'

x25x6ln

5x6x3y'

y1

5x6x2

5x6ln5x6x6y'y1

x5x6y buty

5x6x25x6ln5x6x6y'

x5x6

5x6x25x6ln5x6x6y'

Page 83: R lecture co4_math 21-1

1xx34y .4

x34ln1xyln

x34lny ln 1x

1x21x34ln3

x3411x'y

y1

1x2x34ln

x341x3'y

y1

1xx342

x34lnx341x6'yy1

1xx34y but y1xx342

x34lnx341x6y'

1xx341xx342

x34lnx341x6'y

11xx341x2

x34lnx341x6y'

Page 84: R lecture co4_math 21-1

2xlog3x4xh .1 22

3233 x3xlogxf .2

234 x11x3logxg .3

3 24 2x3xxlnxF .4

)x43log(

x4x3xH .5 3

2

36

4 1xlogx3y .6

A. Differentiate and simplify each of the following:EXERCISES:

Page 85: R lecture co4_math 21-1

B. Differentiate each of the following using implicit differentiation.

1x2

3x4xx3y .1 2

32

5 32 3x41xxf .2

32 x4logyxxylog .1

x2elnylnxxlny .2

C. Differentiate each of the following using logarithmic differentiation.

Page 86: R lecture co4_math 21-1

DIFFERENTIATION OF EXPONENTIAL FUNCTIONS

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The EXPONENTIAL FUNCTION

.ylogx as writtenbe also may ay function, c logarithmi

of inverse the is function l exponentia the Sincenumber. real a is x whereayby defined is 1,a

and 0a a, base withfunction l exponentia The

a

x

x

.

Page 88: R lecture co4_math 21-1

.

nmanama .1

n m if ,m-na1

n m if , 1n m if ,nma

nama .2

mnanma .3

nbnanab .4

nbnan

ba .5

0 a provided ,10a .6 n1ma

mn1anma .7

Laws of Exponents

xa .8 xloga

y x then aa if .9 yx

Page 89: R lecture co4_math 21-1

DIFFERENTIATION FORMULA

Derivative of Exponential Function The derivative of the exponential function for any given base and any differentiable function of u.

f(x)u where;dxdue )e(

dxd

f(x)u where;dxdualna )a(

dxd

uu

uu

:e base For

:abase given any For

Page 90: R lecture co4_math 21-1

A. Find the derivative of each of the following and simplify the result:

2x3exf .1

x21exg .2

x/12ex4xh .3 2

2

x3

x3

xe6x'f

x6ex'f

x212

2ex'g x21

x2ex

1ex4x'h x/12

x/12

EXAMPLE:

x21x21

x21ex'g

x21

x21e4x'h x/1

1x2e4x'h x/1

x21

x21ex'gx21

Page 91: R lecture co4_math 21-1

2yx2xxye .4

02y'yx1yx21y'xyxye

2y'xyyx2yxye'yxyxe

'xyy2xy2xye3y'yxye2xy

2xy2xye3yyxxye2xy'y

xye2y1x

xye2yxy21y'y

Page 92: R lecture co4_math 21-1

5x42x37y .5

5x42x3dx

d7ln5x42x37'y

4x67ln5x42x37'y

5x42x377ln2x32'y

2x34lnxh .6

2x34

2x34dxd

)x('h

2x34

2x3dxd4ln2x34

x'h

x64lnx'h 4lnx6x'h

2x34lnxh

4ln2x3xh

2xdx

d4ln3x'h

x24ln3x'h

4lnx6x'h

OR

Page 93: R lecture co4_math 21-1

3x2e1xelogxG .6

3elog1elogxG x2x

elog3e2eelog

1eex'G x2

x2

x

x

elog

3e1e1ee23eex'G x2x

xx2x2x

eloge3e1e

e2e23ex'G xx2x

xx2x2

eloge3e1e3e2e3x'G x

x2x

xx2

Page 94: R lecture co4_math 21-1

24 xx3 52xf .7

4224 x3xxx3 2dxd55

dxd2x'f

3x3xxx3 x122ln25x25ln52x'f4224

2lnx65ln52x2x'f 2xx3 24

x2lnx65ln52x'f 2x1x3 24

24 xx3 52xf

24 xx3 52lnxfln

24 xx3 5ln2lnxfln

5lnx2lnx3xfln 24

x25lnx42ln3xfx'f 3

5ln2lnx6x2xfx'f 2

5ln2lnx6x252)x('f 2xx3 24

x5ln2lnx652x'f 2x1x3 24

OR

Page 95: R lecture co4_math 21-1

yx53 .8 4yx

'yx4'y5ln53ln3 3yx

3ln3x415ln5'y x3y

15ln5

3ln3x4'y y

x3

Page 96: R lecture co4_math 21-1

A. Find the derivative and simplify the result.

1x3x2

3xg .1

22 xlnxexf .2

2eey .3 x3

x4

3x222 3xlogxh .4

2x5xG.1

2lnyxxeye.2 22yx

2X1xxH.3

1x2ey.4

1x2

x2x2 eelnxf.5

B. Apply the appropriate formulas to obtain the derivative of the given function and simplify.

EXERCISES:

Page 97: R lecture co4_math 21-1

Logarithmic DifferentiationOftentimes, the derivatives of algebraic functions which appear complicated in form (involving products, quotients and powers) can be found quickly by taking the natural logarithms of both sides and applying the properties of logarithms before differentiation. This method is called logarithmic differentiation.

Page 98: R lecture co4_math 21-1

1. Take the natural logarithm of both sides and apply the properties of logarithms.

2. Differentiate both sides and reduce the right side to a single fraction.

3. Solve for y’ by multiplying the right side by y.4. Substitute and simplify the result.

Steps in applying logarithmic differentiation.

Logarithmic differentiation is also applicable wheneverthe base and its power are both functions.

Page 99: R lecture co4_math 21-1

xxy if dx

dy Find .1

xlnxylnxlnyln x

Logarithmic differentiation is also applicable whenever the base and its power are both functions. (Variable to variable power.)

Example:

1xln1x1x'y

y1

xx y butyxln1'y

xxxln1'y

Page 100: R lecture co4_math 21-1

1x2ln1xyln

1x2lnyln 1x

1x1x2y if dx

dy Find .2

11x2ln21x2

11x'yy1

1x2ln1x21x2'y

y1

1-x12x y buty1x2ln1x21x2'y

1-x12x 1x2

1x2ln1x21x2'y

1-1-x12x 1x2ln1x21x2'y

2-x12x 1x2ln1x21x2'y

Page 101: R lecture co4_math 21-1

x5x6y .3

5x6lnxyln

5x6lny lnx

x2

15x6ln5x62

65x6

1xy'y1

12x

5x6x2

5x6ln5x6x6y'

x25x6ln

5x6x3y'

y1

5x6x2

5x6ln5x6x6y'y1

x5x6y buty

5x6x25x6ln5x6x6y'

x5x6

5x6x25x6ln5x6x6y'

Page 102: R lecture co4_math 21-1

1xx34y .4

x34ln1xyln

x34lny ln 1x

1x21x34ln3

x3411x'y

y1

1x2x34ln

x341x3'y

y1

1xx342

x34lnx341x6'yy1

1xx34y but y1xx342

x34lnx341x6y'

1xx341xx342

x34lnx341x6'y

11xx341x2

x34lnx341x6y'

Page 103: R lecture co4_math 21-1

References

Calculus, Early Transcendental Functions, by Larson and EdwardsCalculus, Early Transcendentals, by Anton, Bivens and DavisUniversity Calculus, Early Transcendentals 2nd ed, by Hass, Weir and ThomasDifferential and Integral Calculus by Love and Rainville