Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation

and i

exp(x) = inverse of ln(x)

Last day, we saw that the function f (x) = ln x is one-to-one, with domain
(0, ∞) and range (−∞, ∞). 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 definition of inverse functions gives us the following:

y = f −1 (x) if and only if x = f (y )

y = exp(x) if and only if x = ln(y )

The cancellation laws give us:

f −1 (f (x)) = x and f (f −1 (x)) = x

exp(ln x) = x and ln(exp(x)) = x .

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Graph of exp(x)
We can draw the graph of y = exp(x) by reflecting the graph of y = ln(x) in
the line y = x.

have that the graph y = exp(x) is

one-to-one and continuous with
20
domain (−∞, ∞) and range (0, ∞).
Note that exp(x) > 0 for all values of
x. We see that
15 y = expHxL = ex
exp(0) = 1 since ln 1 = 0
exp(1) = e since ln e = 1,
exp(2) = e 2 since ln(e 2 ) = 2,
10
exp(−7) = e −7 since ln(e −7 ) = −7.
H2, e2 L
In fact for any rational number r , we
5
have
exp(r ) = e r since ln(e r ) = r ln e =
H1, eL y = lnHxL
r,
H-7, e-7 L H0, 1L He2 , 2L
He, 1L
H1, 0L
by the laws of Logarithms.
-5 5 10

-5

He-7Annette
, -7L Pilkington Natural Logarithm and Natural Exponential
Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Definition of e x .

Definition When x is rational or irrational, we define e x to be exp(x).

e x = exp(x)

Note: This agrees with definitions of e x given elsewhere (as limits), since the
definition is the same when x is 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:
When f (x) = ln(x), f −1 (x) = e x and

e x = y if and only if ln y = x

e ln x = x and ln e x = x

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Solving Equations
We can use the formula below to solve equations involving logarithms and
exponentials.
e ln x = x and ln e x = x
Example Solve for x if ln(x + 1) = 5

Example Solve for x if e x−4 = 10

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Solving Equations
We can use the formula below to solve equations involving logarithms and
exponentials.
e ln x = x and ln e x = x
Example Solve for x if ln(x + 1) = 5
I Applying the exponential function to both sides of the equation
ln(x + 1) = 5, we get
e ln(x+1) = e 5

Example Solve for x if e x−4 = 10

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Solving Equations
We can use the formula below to solve equations involving logarithms and
exponentials.
e ln x = x and ln e x = x
Example Solve for x if ln(x + 1) = 5
I Applying the exponential function to both sides of the equation
ln(x + 1) = 5, we get
e ln(x+1) = e 5
I Using the fact that e ln u = u, (with u = x + 1 ), we get

x + 1 = e5, or x = e5 − 1 .

Example Solve for x if e x−4 = 10

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Solving Equations
We can use the formula below to solve equations involving logarithms and
exponentials.
e ln x = x and ln e x = x
Example Solve for x if ln(x + 1) = 5
I Applying the exponential function to both sides of the equation
ln(x + 1) = 5, we get
e ln(x+1) = e 5
I Using the fact that e ln u = u, (with u = x + 1 ), we get

x + 1 = e5, or x = e5 − 1 .

Example Solve for x if e x−4 = 10

I Applying the natural logarithm function to both sides of the equation
e x−4 = 10, we get
ln(e x−4 ) = ln(10)

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Solving Equations
We can use the formula below to solve equations involving logarithms and
exponentials.
e ln x = x and ln e x = x
Example Solve for x if ln(x + 1) = 5
I Applying the exponential function to both sides of the equation
ln(x + 1) = 5, we get
e ln(x+1) = e 5
I Using the fact that e ln u = u, (with u = x + 1 ), we get

x + 1 = e5, or x = e5 − 1 .

Example Solve for x if e x−4 = 10

I Applying the natural logarithm function to both sides of the equation
e x−4 = 10, we get
ln(e x−4 ) = ln(10)
I Using the fact that ln(e u ) = u, (with u = x − 4) , we get
x − 4 = ln(10), or x = ln(10) + 4.
Annette Pilkington Natural Logarithm and Natural Exponential
Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Limits

From the graph we see that

lim e x = 0, lim e x = ∞.
x→−∞ x→∞

ex
Example Find the limit limx→∞ 10e x −1
.

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Limits

From the graph we see that

lim e x = 0, lim e x = ∞.
x→−∞ x→∞

ex
Example Find the limit limx→∞ 10e x −1
.
I As it stands, this limit has an indeterminate form since both numerator
and denominator approach infinity as x → ∞

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Limits

From the graph we see that

lim e x = 0, lim e x = ∞.
x→−∞ x→∞

ex
Example Find the limit limx→∞ 10e x −1
.
I As it stands, this limit has an indeterminate form since both numerator
and denominator approach infinity as x → ∞
I We modify a trick from Calculus 1 and divide (both Numertor and
denominator) by the highest power of e x in the denominator.

ex e x /e x
lim = lim
x→∞ 10e − 1
x x→∞ (10e x − 1)/e x

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Limits

From the graph we see that

lim e x = 0, lim e x = ∞.
x→−∞ x→∞

ex
Example Find the limit limx→∞ 10e x −1
.
I As it stands, this limit has an indeterminate form since both numerator
and denominator approach infinity as x → ∞
I We modify a trick from Calculus 1 and divide (both Numertor and
denominator) by the highest power of e x in the denominator.

ex e x /e x
lim = lim
x→∞ 10e − 1
x x→∞ (10e x − 1)/e x

I
1 1
= lim =
x→∞ 10 − (1/e x ) 10

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Rules of exponentials

The following rules of exponents follow from the rules of logarithms:

ex
e x+y = e x e y , e x−y = , (e x )y = e xy .
ey

Proof see notes for details

2
e x e 2x+1
Example Simplify (e x )2
.

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Rules of exponentials

The following rules of exponents follow from the rules of logarithms:

ex
e x+y = e x e y , e x−y = , (e x )y = e xy .
ey

Proof see notes for details

2
e x e 2x+1
Example Simplify (e x )2
.
I
2 2
e x e 2x+1 e x +2x+1
x 2
=
(e ) e 2x

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Rules of exponentials

The following rules of exponents follow from the rules of logarithms:

ex
e x+y = e x e y , e x−y = , (e x )y = e xy .
ey

Proof see notes for details

2
e x e 2x+1
Example Simplify (e x )2
.
I
2 2
e x e 2x+1 e x +2x+1
x 2
=
(e ) e 2x
I
2 2
= ex +2x+1−2x
= ex +1

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Derivatives

d x d g (x)
e = ex e = g 0 (x)e g (x)
dx dx

Proof We use logarithmic differentiation. If y = e x , we have ln y = x and

differentiating, we get y1 dy
dx
= 1 or dy
dx
= y = e x . The derivative on the right
follows from the chain rule.
d sin2 x
Example Find dx
e

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Derivatives

d x d g (x)
e = ex e = g 0 (x)e g (x)
dx dx

Proof We use logarithmic differentiation. If y = e x , we have ln y = x and

differentiating, we get y1 dy
dx
= 1 or dy
dx
= y = e x . The derivative on the right
follows from the chain rule.
d sin2 x
Example Find dx
e
I Using the chain rule, we get
d sin2 x 2 d
e = e sin x · sin2 x
dx dx

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Derivatives

d x d g (x)
e = ex e = g 0 (x)e g (x)
dx dx

Proof We use logarithmic differentiation. If y = e x , we have ln y = x and

differentiating, we get y1 dy
dx
= 1 or dy
dx
= y = e x . The derivative on the right
follows from the chain rule.
d sin2 x
Example Find dx
e
I Using the chain rule, we get
d sin2 x 2 d
e = e sin x · sin2 x
dx dx
I
2 2
= e sin x 2(sin x)(cos x) = 2(sin x)(cos x)e sin x

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Derivatives

d x d g (x)
e = ex e = g 0 (x)e g (x)
dx dx

2
Example Find d
dx
sin2 (e x )

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Derivatives

d x d g (x)
e = ex e = g 0 (x)e g (x)
dx dx

2
Example Find d
dx
sin2 (e x )
I Using the chain rule, we get
d 2 2 d 2
sin2 (e x ) = 2 sin(e x ) · sin(e x )
dx dx

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Derivatives

d x d g (x)
e = ex e = g 0 (x)e g (x)
dx dx

2
Example Find d
dx
sin2 (e x )
I Using the chain rule, we get
d 2 2 d 2
sin2 (e x ) = 2 sin(e x ) · sin(e x )
dx dx
I
2 2 d x2
= 2 sin(e x ) cos(e x ) · e
dx

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Derivatives

d x d g (x)
e = ex e = g 0 (x)e g (x)
dx dx

2
Example Find d
dx
sin2 (e x )
I Using the chain rule, we get
d 2 2 d 2
sin2 (e x ) = 2 sin(e x ) · sin(e x )
dx dx
I
2 2 d x2
= 2 sin(e x ) cos(e x ) · e
dx
I
2 2 2 d 2 2 2 2
= 2 sin(e x ) cos(e x )e x · x = 4xe x sin(e x ) cos(e x )
dx

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Integrals

Z Z
e x dx = e x + C g 0 (x)e g (x) dx = e g (x) + C

2
xe x +1
R
Example Find dx.

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Integrals

Z Z
e x dx = e x + C g 0 (x)e g (x) dx = e g (x) + C

2
xe x +1
R
Example Find dx.
I Using substitution, we let u = x 2 + 1.
du
du = 2x dx, = x dx
2

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Integrals

Z Z
e x dx = e x + C g 0 (x)e g (x) dx = e g (x) + C

2
xe x +1
R
Example Find dx.
I Using substitution, we let u = x 2 + 1.
du
du = 2x dx, = x dx
2
I Z Z Z
2 du 1 1 u
xe x +1
dx = eu = e u du = e +C
2 2 2

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Integrals

Z Z
e x dx = e x + C g 0 (x)e g (x) dx = e g (x) + C

2
xe x +1
R
Example Find dx.
I Using substitution, we let u = x 2 + 1.
du
du = 2x dx, = x dx
2
I Z Z Z
2 du 1 1 u
xe x +1
dx = eu = e u du = e +C
2 2 2
I Switching back to x, we get
1 x 2 +1
= e +C
2

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Summary of formulas

ln(x) ex

a ln e x = x and e ln(x) = x
ln(ab) = ln a+ln b, ln( ) = ln a−ln b
b
ln ax = x ln a ex
e x+y = e x e y , e x−y = , (e x )y = e xy .
ey
lim ln x = ∞, lim ln x = −∞
x→∞ x→0 lim e x = ∞, and lim e x = 0
x→∞ x→−∞

d 1 d g 0 (x) d x d g (x)
ln |x| = , ln |g (x)| = e = ex , e = g 0 (x)e g (x)
dx x dx g (x) dx dx
Z
1 Z
dx = ln |x| + C e x dx = e x + C
x
Z 0
g (x)
Z
dx = ln |g (x)| + C . g 0 (x)e g (x) dx = e g (x) + C
g (x)

Annette Pilkington Natural Logarithm and Natural Exponential

Natural Logarithm Function Graph of Natural Logarithm Algebraic Properties of ln(x) Limits Extending the antiderivative of 1/x Differentiation and i

Summary of methods

Logarithmic Differentiation
Solving equations
(Finding formulas for inverse functions)
Finding slopes of inverse functions (using formula from lecture 1).
Calculating Limits
Calculating Derivatives
Calculating Integrals (including definite integrals)

Annette Pilkington Natural Logarithm and Natural Exponential