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54 Exponential Functions: Differentiation and Integration

f x xln is called the natural exponential function and is denoted by f x e 1 x That is, yex if and only if xy ln Properties of the Natural Exponential Function: 1 The domain of f x ex , is f f , and the range is 0,f 2 The function f x ex is continuous, increasing, and one-to-one on its entire domain 3 The graph of f x ex



exp(x) = inverse of ln(x

Last day, we saw that the function f (x) = lnx is one-to-one, with domain (0;1) and range (1 ;1) We can conclude that f (x) has an inverse function which we call the natural exponential function and denote (temorarily) by f 1(x) = exp(x), The de nition of inverse functions gives us the following: y = f 1(x) if and only if x = f (y)



(25 points) f x

1 (25 points) Sketch a graph of the function f(x) = xln(x) x Your work should include: - Domain - Intercepts - Symmetry - Asymptotes (no Slant asymptotes, though) - Intervals of increase/decrease/local max/min - Concavity and inflection points (1) Domain: x>0 (2) No y intercepts, x intercept x= e(f(x) = 0 ,xln(x) x= 0 ,xln(x) = x,ln(x) = 1



Section 109: Applications of Taylor Polynomials f x a

The derivatives of f(x) are f(x) = ln(x) f(3) = ln(3) f0(x) = 1 x f0(3) = 1 3 f00(x) = 1 x2 f00(3) = 1 9 f000(x) = 2 x3 f000(3) = 2 27: So the third degree Taylor polynomial is T 3(x) = ln(3) + 1 3 (x 3) 1 18 (x 3)2 + 1 81 (x 3)3: (b) Use Taylor’s Inequality to estimate the accuracy of the approximation f(x) ˇT 3(x) for 2 x 4 The fourth



AP Calculus BC - College Board

6 The Maclaurin series for ln(l + x) is given by x 2 x 3 x 4 +1X n x--+---+ ·+(-lf -+ · 2 3 4 n On its interval of convergence, this series converges to lo ( 1 + x ) Let f be the function defined, by 'f(x) = x1n(1 + 1} (a) Write the first four nonzero terms and the general term of the Maclaurin series for f +-ti\ · ·r--,/\- ; k



59 Representations of Functions as a Power Series

Given the function f(x) = X1 0 c n(x a)n, whose domain is the interval of convergence Theorem 5 7 If a power series P c n(x a)n has radius R > 0, then f(x) = X1 0 = c 0 + c 1(x a) + c 2(x a)2 + c 3(x a)3 + ::: is di erentiable on (a R;a+ R), and 1 f0(x) = c 1 + 2c 2(x a) + 3c 3(x a)2 + 4c 4(x a)3 + ::: = X nc n(x a)n 1 2 Z f(x) dx = c+ c 0



Approximating functions by Taylor Polynomials

2(x) has the same first and second derivative that f (x) does at the point x = a 4 3 Higher Order Taylor Polynomials We get better and better polynomial approximations by using more derivatives, and getting higher degreed



Absolute Maximum and Minimum - Texas A&M University

2 Find the absolute maximum and absolute minimum values of f on the given interval f(x)=x+ 9 x on [0 2,12] 3 Find the absolute minimum and absolute maximum values of f on the given interval

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exp(x) = inverse of ln(x) Last day, we saw that the functionf(x) = lnxis one-to-one, with domain (0;1) and range (1;1). We can conclude thatf(x) has an inverse function which we call the natural exponential function and denote (temorarily) byf1(x) = exp(x), The denition of inverse functions gives us the following: y=f1(x) if and only ifx=f(y) y= exp(x) if and only ifx= ln(y)The cancellation laws give us: f

1(f(x)) =xandf(f1(x)) =x

exp(lnx) =xand ln(exp(x)) =x: Annette PilkingtonNatural Logarithm and Natural Exponential

Graph of exp(x)

We can draw the graph ofy=exp(x) by re

ecting the graph ofy=ln(x) in the liney=x.He2,2LH2,e2LH1,0LH0,1LHe,1LH1,eLHe-7,-7LH-7,e-7Ly=expHxL=exy=lnHxL-5510-10-55101520

Wehave that the graphy= exp(x) is

one-to-one and continuous with domain (1;1) and range (0;1).

Note that exp(x)>0 for all values of

x. We see that exp(0) = 1 since ln1 = 0 exp(1) =esince lne= 1; exp(2) =e2since ln(e2) = 2; exp(7) =e7since ln(e7) =7:

In fact for any rational numberr, we

have exp(r) =ersince ln(er) =rlne= r; by the laws of Logarithms. Annette PilkingtonNatural Logarithm and Natural Exponential

Denition ofex.

DenitionWhenxis rational or irrational, we deneexto be exp(x). e x= exp(x)Note:This agrees with denitions ofexgiven elsewhere (as limits), since the denition is the same whenxis a rational number and the exponential function is continuous. Restating the above properties given above in light of this new interpretation of the exponential function, we get:

Whenf(x) = ln(x),f1(x) =exand

e x=yif and only if lny=xe lnx=xand lnex=xAnnette PilkingtonNatural Logarithm and Natural Exponential

Solving Equations

We can use the formula below to solve equations involving logarithms and exponentials. e lnx=xand lnex=xExampleSolve forxif ln(x+ 1) = 5I Applying the exponential function to both sides of the equation ln(x+ 1) = 5, we get e ln(x+1)=e5I

Using the fact that elnu=u, (with u=x+ 1), we get

x+ 1 =e5;or x=e51:

ExampleSolve forxifex4= 10I

Applying the natural logarithm function to both sides of the equation e x4= 10, we get ln(ex4) = ln(10)I Using the fact thatln(eu) =u, (with u=x4) , we get x4 = ln(10);or x= ln(10) + 4:Annette PilkingtonNatural Logarithm and Natural Exponential

Limits

From the graph we see that

lim x!1ex= 0;limx!1ex=1:ExampleFind the limit limx!1ex10ex1.I As it stands, this limit has an indeterminate form since both numerator and denominator approach innity as x! 1I We modify a trick from Calculus 1 and divide (both Numertor and denominator) by the highest power of e xin the denominator. lim x!1e x10ex1= limx!1e x=ex(10ex1)=exI = lim x!1110(1=ex)=110 Annette PilkingtonNatural Logarithm and Natural Exponential

Rules of exponentials

The following rules of exponents follow from the rules of logarithms: e x+y=exey;exy=exe y;(ex)y=exy:Proofsee notes for details

ExampleSimplifyex2e2x+1(ex)2.I

e x2e2x+1(ex)2=ex2+2x+1e 2xI =ex2+2x+12x=ex2+1Annette PilkingtonNatural Logarithm and Natural Exponential

Derivatives

ddx ex=exd dx eg(x)=g0(x)eg(x)ProofWe use logarithmic dierentiation. Ify=ex, we have lny=xand dierentiating, we get 1y dydx = 1 ordydx =y=ex. The derivative on the right follows from the chain rule.

ExampleFindddx

esin2xI

Using the chain rule, we get

ddx esin2x=esin2xddx sin2xI

=esin2x2(sinx)(cosx) = 2(sinx)(cosx)esin2xAnnette PilkingtonNatural Logarithm and Natural Exponential

Derivatives

ddx ex=exd dx eg(x)=g0(x)eg(x)ExampleFindddx sin2(ex2)I

Using the chain rule, we get

ddx sin2(ex2) = 2sin(ex2)ddx sin(ex2)I = 2sin(ex2)cos(ex2)ddx ex2I = 2sin(ex2)cos(ex2)ex2ddx x2= 4xex2sin(ex2)cos(ex2)Annette PilkingtonNatural Logarithm and Natural Exponential

Integrals

Z e xdx=ex+CZ g

Using substitution, we let u=x2+ 1.

du= 2x dx;du2 =x dxI Z xe x2+1dx=Z e udu2 =12 Z e udu=12 eu+CI

Switching back to x, we get

12 ex2+1+CAnnette PilkingtonNatural Logarithm and Natural Exponential

Summary of formulas

ln(x)ln(ab) = lna+lnb;ln(ab ) = lnalnb lnax=xlna lim x!1lnx=1;limx!0lnx=1 ddx lnjxj=1x ;ddx lnjg(x)j=g0(x)g(x) Z1x dx= lnjxj+C

Zg0(x)g(x)dx= lnjg(x)j+C:e

xlnex=xandeln(x)=x e x+y=exey;exy=exe y;(ex)y=exy: lim x!1ex=1;and limx!1ex= 0 ddx ex=ex;ddx eg(x)=g0(x)eg(x) Z e xdx=ex+C Z g

0(x)eg(x)dx=eg(x)+CAnnette PilkingtonNatural Logarithm and Natural Exponential

Summary of methods

Logarithmic Dierentiation

Solving equations

(Finding formulas for inverse functions) Finding slopes of inverse functions (using formula from lecture 1).

Calculating Limits

Calculating Derivatives

Calculating Integrals (including denite integrals) Annette PilkingtonNatural Logarithm and Natural Exponentialquotesdbs_dbs5.pdfusesText_10