Ap Calculus Bc Mixed Review Pdf Substitution Natural Log Logarithmic Differentiation
3. Derivatives
3.9 Derivatives of Exponential and Logarithmic Functions
Learning Objectives
- Notice the derivative of exponential functions.
- Notice the derivative of logarithmic functions.
- Utilise logarithmic differentiation to determine the derivative of a function.
So far, we take learned how to differentiate a variety of functions, including trigonometric, inverse, and implicit functions. In this section, we explore derivatives of exponential and logarithmic functions. As nosotros discussed in Introduction to Functions and Graphs, exponential functions play an important role in modeling population growth and the decay of radioactive materials. Logarithmic functions can help rescale large quantities and are particularly helpful for rewriting complicated expressions.
Derivative of the Exponential Function
Merely as when we found the derivatives of other functions, we can find the derivatives of exponential and logarithmic functions using formulas. As we develop these formulas, we need to brand certain basic assumptions. The proofs that these assumptions concord are across the telescopic of this class.
Showtime of all, nosotros begin with the assumption that the part , is defined for every real number and is continuous. In previous courses, the values of exponential functions for all rational numbers were defined—showtime with the definition of
, where
is a positive integer—every bit the product of
multiplied past itself
times. Later, we defined
for a positive integer
, and
for positive integers
and
. These definitions leave open the question of the value of
where
is an arbitrary real number. By bold the continuity of
, we may interpret
as
where the values of
as we have the limit are rational. For example, we may view
every bit the number satisfying
As we see in the following table, .
![]() | ![]() | ![]() | ![]() |
---|---|---|---|
![]() | 64 | ![]() | 77.8802710486 |
![]() | 73.5166947198 | ![]() | 77.8810268071 |
![]() | 77.7084726013 | ![]() | 77.9242251944 |
![]() | 77.8162741237 | ![]() | 78.7932424541 |
![]() | 77.8702309526 | ![]() | 84.4485062895 |
![]() | 77.8799471543 | ![]() | 256 |
We also assume that for , the value
of the derivative exists. In this section, we show that by making this one boosted assumption, it is possible to prove that the function
is differentiable everywhere.
Nosotros make one final assumption: that there is a unique value of for which
. We ascertain
to be this unique value, as we did in Introduction to Functions and Graphs. (Figure) provides graphs of the functions
, and
. A visual estimate of the slopes of the tangent lines to these functions at 0 provides evidence that the value of
lies somewhere between 2.vii and 2.8. The office
is called the natural exponential office. Its changed,
is called the natural logarithmic function.
For a better estimate of , we may construct a table of estimates of
for functions of the form
. Earlier doing this, recall that
for values of very close to nix. For our estimates, we choose
and
to obtain the judge
.
Meet the following tabular array.















The testify from the table suggests that .
The graph of together with the line
are shown in (Figure). This line is tangent to the graph of
at
.
At present that we accept laid out our basic assumptions, we begin our investigation by exploring the derivative of . Retrieve that we have assumed that
exists. By applying the limit definition to the derivative we conclude that
.
Turning to , we obtain the following.
Nosotros come across that on the footing of the assumption that is differentiable at
is not only differentiable everywhere, but its derivative is
.
For . Thus, we have
. (The value of
for an arbitrary role of the class
, will be derived later.)
Derivative of the Natural Exponential Office
Let be the natural exponential function. Then
.
In general,
.
Derivative of an Exponential Function
Find the derivative of .
Solution
Using the derivative formula and the chain rule,
Combining Differentiation Rules
Observe the derivative of .
Solution
Use the derivative of the natural exponential part, the quotient dominion, and the chain rule.
Find the derivative of .
Solution
Applying the Natural Exponential Function
A colony of mosquitoes has an initial population of 1000. After days, the population is given by
. Show that the ratio of the rate of modify of the population,
, to the population size,
is constant.
Solution
First observe . By using the chain dominion, we take
. Thus, the ratio of the charge per unit of alter of the population to the population size is given by
.
The ratio of the charge per unit of modify of the population to the population size is the constant 0.3.
Derivative of the Logarithmic Function
Now that we take the derivative of the natural exponential function, we can apply implicit differentiation to find the derivative of its inverse, the natural logarithmic function.
The Derivative of the Natural Logarithmic Office
If and
, then
.
More generally, let be a differentiable function. For all values of
for which
, the derivative of
is given past
.
Proof
If and
, then
. Differentiating both sides of this equation results in the equation
.
Solving for yields
.
Finally, we substitute to obtain
.
We may also derive this result by applying the inverse part theorem, as follows. Since is the inverse of
, by applying the inverse function theorem we have
.
Using this outcome and applying the concatenation rule to yields
The graph of and its derivative
are shown in (Figure).
Taking a Derivative of a Natural Logarithm
Observe the derivative of .
Solution
Use (Figure) directly.
Using Backdrop of Logarithms in a Derivative
Detect the derivative of .
Solution
At outset glance, taking this derivative appears rather complicated. However, by using the properties of logarithms prior to finding the derivative, we can make the trouble much simpler.
Differentiate: .
Solution
At present that we can differentiate the natural logarithmic function, nosotros tin can use this result to observe the derivatives of and
for
.
Derivatives of General Exponential and Logarithmic Functions
Let , and let
exist a differentiable office.
- If
, so
.
More by and large, if
, then for all values of
for which
,
.
- If
, then
.
More by and large, if
, then
.
Proof
If , then
. Information technology follows that
. Thus
. Solving for
, we take
. Differentiating and keeping in mind that
is a abiding, we meet that
.
The derivative in (Figure) now follows from the chain dominion.
If , so
. Using implicit differentiation, once more keeping in mind that
is constant, it follows that
Solving for
and substituting
, we come across that
.
The more than general derivative ((Effigy)) follows from the chain rule.
Applying Derivative Formulas
Detect the derivative of .
Solution
Use the quotient rule and (Figure).
Finding the Slope of a Tangent Line
Find the slope of the line tangent to the graph of at
.
Solution
To notice the slope, we must evaluate at
. Using (Figure), we encounter that
.
By evaluating the derivative at , we see that the tangent line has slope
.
Find the slope for the line tangent to at
.
Solution
Logarithmic Differentiation
At this point, we can take derivatives of functions of the form for certain values of
, too every bit functions of the form
, where
and
. Unfortunately, we notwithstanding do not know the derivatives of functions such as
or
. These functions crave a technique called logarithmic differentiation, which allows us to differentiate any function of the grade
. It can also be used to catechumen a very complex differentiation trouble into a simpler i, such as finding the derivative of
. Nosotros outline this technique in the following trouble-solving strategy.
Using Logarithmic Differentiation
Find the derivative of .
Solution
Use logarithmic differentiation to observe this derivative.
Using Logarithmic Differentiation
Observe the derivative of .
Solution
This problem really makes use of the properties of logarithms and the differentiation rules given in this affiliate.
Extending the Power Rule
Detect the derivative of where
is an arbitrary existent number.
Solution
The procedure is the aforementioned as in (Effigy), though with fewer complications.
Use logarithmic differentiation to find the derivative of .
Solution
Find the derivative of .
Solution
Key Concepts
Fundamental Equations
For the following exercises, find for each function.
1.
Solution
two.
three.
Solution
iv.
five.
Solution
6.
7.
Solution
viii.
ix.
Solution
ten.
11.
Solution
12.
13.
Solution
14.
xv.
Solution
For the post-obit exercises, utilize logarithmic differentiation to find .
16.
17.
Solution
18.
19.
Solution
twenty.
21.
Solution
22.
23.
Solution
24. [T] Observe an equation of the tangent line to the graph of at the point where
. Graph both the office and the tangent line.
25. [T] Find the equation of the line that is normal to the graph of at the point where
. Graph both the function and the normal line.
Solution
29. [T] The population of Toledo, Ohio, in 2000 was approximately 500,000. Presume the population is increasing at a rate of 5% per year.
- Write the exponential function that relates the total population as a role of
.
- Use a. to determine the rate at which the population is increasing in
years.
- Use b. to determine the rate at which the population is increasing in x years.
Solution
a. individuals
b. individuals per year
c. 39,737 individuals per year
Solution
a. At the beginning of 1960 there were 5.3 thousand cases of the disease in New York Urban center. At the beginning of 1963 there were approximately 723 cases of the disease in New York City.
b. At the commencement of 1960 the number of cases of the disease was decreasing at rate of -4.611 1000 per year; at the start of 1963, the number of cases of the disease was decreasing at a rate of -0.2808 thousand per year.
For the following exercises, use the population of New York Metropolis from 1790 to 1860, given in the post-obit table.
Years since 1790 | Population |
0 | 33,131 |
10 | 60,515 |
20 | 96,373 |
30 | 123,706 |
40 | 202,300 |
50 | 312,710 |
sixty | 515,547 |
70 | 813,669 |
33. [T] Using a figurer program or a calculator, fit a growth curve to the information of the form .
Solution
34. [T] Using the exponential best fit for the data, write a table containing the derivatives evaluated at each year.
35. [T] Using the exponential best fit for the data, write a table containing the second derivatives evaluated at each year.
Solution
Years since 1790 | ![]() |
---|---|
0 | 69.25 |
10 | 107.5 |
20 | 167.0 |
30 | 259.4 |
40 | 402.eight |
50 | 625.5 |
lx | 971.four |
70 | 1508.5 |
36. [T] Using the tables of commencement and second derivatives and the best fit, answer the post-obit questions:
- Volition the model be accurate in predicting the future population of New York City? Why or why not?
- Estimate the population in 2010. Was the prediction correct from a.?
Glossary
- logarithmic differentiation
- is a technique that allows u.s. to differentiate a office by first taking the natural logarithm of both sides of an equation, applying properties of logarithms to simplify the equation, and differentiating implicitly
Source: https://opentextbc.ca/calculusv1openstax/chapter/derivatives-of-exponential-and-logarithmic-functions/
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