AP Calculus BC : Asymptotic and Unbounded Behavior

Study concepts, example questions & explanations for AP Calculus BC

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Example Questions

Example Question #1 : Asymptotic And Unbounded Behavior

A cylinder of height \(\displaystyle 4in\) and radius \(\displaystyle 1in\) is expanding. The radius increases at a rate of \(\displaystyle 0.1\frac{in}{s}\) and its height increases at a rate of \(\displaystyle 0.2\frac{in}{s}\). What is the rate of growth of its surface area?

Possible Answers:

\(\displaystyle 0.4\pi\frac{in^2}{s}\)

\(\displaystyle 1.4\pi\frac{in^2}{s}\)

\(\displaystyle 2.8\pi\frac{in^2}{s}\)

\(\displaystyle 1.6\pi\frac{in^2}{s}\)

\(\displaystyle 0.2\pi\frac{in^2}{s}\)

Correct answer:

\(\displaystyle 1.6\pi\frac{in^2}{s}\)

Explanation:

The surface area of a cylinder is given by the formula:

\(\displaystyle A=2\pi r^2+2\pi rh\)

To find the rate of growth over time, take the derivative of each side with respect to time:

\(\displaystyle \frac{dA}{dt}=4\pi r \frac{dr}{dt}+2\pi h \frac{dr}{dt} + 2\pi r \frac{dh}{dt}\)

Therefore, the rate of growth of surface area is:

\(\displaystyle \frac{dA}{dt}=4\pi (1in)\left(0.1\frac{in}{s}\right)+2\pi(1in)(4in)\left(0.1\frac{in}{s}\right)+2\pi(1in)\left(0.2\frac{in}{s}\right)\)

\(\displaystyle \frac{dA}{dt}=(0.4\pi+0.8\pi+0.4\pi)\frac{in^2}{s}=1.6\pi\frac{in^2}{s}\)

Example Question #2 : Asymptotic And Unbounded Behavior

The rate of growth of the population of Reindeer in Norway is proportional to the population. The population increased from 9876 to 10381 between 2013 and 2015. What is the expected population in 2030?

Possible Answers:

\(\displaystyle 38914\)

\(\displaystyle 42581\)

\(\displaystyle 49362\)

\(\displaystyle 53880\)

\(\displaystyle 15150\)

Correct answer:

\(\displaystyle 15150\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 9876 to 10381 between 2013 and 2015, we can solve for this constant of proportionality:

\(\displaystyle 10381=9876e^{k(2015-2013)}\)

\(\displaystyle \frac{10381}{9876}=e^{2k}\)

\(\displaystyle 2k=ln(\frac{10381}{9876})\)

\(\displaystyle k=\frac{ln(\frac{10381}{9876})}{2}=0.0252\)

Using this, we can calculate the expected value from 2015 to 2030:

\(\displaystyle P=10381e^{(2030-2015)(0.0252)} \approx 15150\)

Example Question #3 : Asymptotic And Unbounded Behavior

The rate of decrease due to poaching of the elephants in unprotected Sahara is proportional to the population. The population in one region decreased from 1038 to 817 between 2010 and 2015. What is the expected population in 2017?

Possible Answers:

\(\displaystyle 742\)

\(\displaystyle 779\)

\(\displaystyle 619\)

\(\displaystyle 493\)

\(\displaystyle 527\)

Correct answer:

\(\displaystyle 742\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population decreased from 1038 to 817 between 2010 and 2015, we can solve for this constant of proportionality:

\(\displaystyle 817=1038e^{k(2015-2010)}\)

\(\displaystyle \frac{817}{1038}=e^{5k}\)

\(\displaystyle 5k=ln(\frac{817}{1038})\)

\(\displaystyle k=\frac{ln(\frac{817}{1038})}{5}=-0.048\)

Using this, we can calculate the expected value from 2015 to 2017:

\(\displaystyle P=817e^{(2017-2015)(-0.048)} \approx 742\)

Example Question #1 : Identifying Asymptotes Graphically

Asymptoteplot

\(\displaystyle \begin{align*}&\text{Decide which of the following functions, most likely represents the graph above.}\end{align*}\)

Possible Answers:

\(\displaystyle \frac{(13x - 9)}{(17x - 2)}\)

\(\displaystyle \frac{(13x + 9)}{(17x + 2)}\)

\(\displaystyle \frac{(17x - 2)}{(13x - 9)}\)

\(\displaystyle \frac{(17x + 2)}{(13x + 9)}\)

Correct answer:

\(\displaystyle \frac{(13x - 9)}{(17x - 2)}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Observation of the graph shows that there’s a sharp increase}\\&\text{and decrease on either side of a particular x-value. This type}\\&\text{of behavior is observed when there’s a vertical asymptote. An}\\&\text{asymptote is a value that a function may approach, but will}\\&\text{never actually attain. In the case of vertical asymptotes, this}\\&\text{behavior occurs if the function approaches infinity for a given}\\&\text{x-value, often when a zero value appears in a denominator. Noting}\\&\text{this rule, the above function has a zero in the denominator}\\&\text{at a definite point:}\\&x=\frac{2}{17}\\&\text{We find a zero denominator for the function: }\\&\frac{(13x - 9)}{(17x - 2)}\end{align*}\)

Example Question #1 : Asymptotic And Unbounded Behavior

Asymptoteplot

\(\displaystyle \begin{align*}&\text{Which of the four following functions is depicted in the graph above?}\end{align*}\)

Possible Answers:

\(\displaystyle \frac{(14x + 19)}{(4x - 18)}\)

\(\displaystyle \frac{(4x - 18)}{(14x + 19)}\)

\(\displaystyle \frac{(14x - 19)}{(4x + 18)}\)

\(\displaystyle \frac{(4x + 18)}{(14x - 19)}\)

Correct answer:

\(\displaystyle \frac{(4x + 18)}{(14x - 19)}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Observation of the graph shows that there’s a sharp increase}\\&\text{and decrease on either side of a particular x-value. This type}\\&\text{of behavior is observed when there’s a vertical asymptote. An}\\&\text{asymptote is a value that a function may approach, but will}\\&\text{never actually attain. In the case of vertical asymptotes, this}\\&\text{behavior occurs if the function approaches infinity for a given}\\&\text{x-value, often when a zero value appears in a denominator. Noting}\\&\text{this rule, the above function has a zero in the denominator}\\&\text{at a definite point centered around:}\\&x=1.3\\&\text{We find a zero denominator for the function: }\\&\frac{(4x + 18)}{(14x - 19)}\end{align*}\)

Example Question #1 : Asymptotic And Unbounded Behavior

Asymptoteplot

\(\displaystyle \begin{align*}&\text{Which of the four following functions is depicted in the graph above?}\end{align*}\)

Possible Answers:

\(\displaystyle -\frac{(5x + 12)}{(6x - 10)}\)

\(\displaystyle -\frac{(6x - 10)}{(5x + 12)}\)

\(\displaystyle \frac{(12x - 5)}{(10x + 6)}\)

\(\displaystyle \frac{(18x + 6)}{(12x - 5)}\)

Correct answer:

\(\displaystyle -\frac{(5x + 12)}{(6x - 10)}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Notice that as x increases, the function graphed appears to}\\&\text{level out, flattening towards a certain value. This value is}\\&\text{what is known as a horizontal asymptote. An asymptote is a value}\\&\text{that a function approaches, but never actually reaches. Think}\\&\text{of a horizontal asymptote as the limit of a function as x approaches}\\&\text{infinity. In such a case, as x approaches infinity, any constants}\\&\text{added or subtracted in the numerator and denominator become}\\&\text{irrelevant. What matters is the power of x in the denominator}\\&\text{and the numerator; if those are the same, then the coefficients}\\&\text{define the asymptote. We see that the function flattens towards:}\\&f(\infty)=-0.8\\&\text{This matches the ratio of coefficients for the function: }\\&-\frac{(5x + 12)}{(6x - 10)}\end{align*}\)

Example Question #64 : Functions, Graphs, And Limits

Asymptoteplot

\(\displaystyle \begin{align*}&\text{Of the following functions, which most likely represents the graph above?}\end{align*}\)

Possible Answers:

\(\displaystyle -\frac{(3x - 2)}{(10x - 11)}\)

\(\displaystyle \frac{(10x - 11)}{(3x - 2)}\)

\(\displaystyle -\frac{(10x - 11)}{(3x - 2)}\)

\(\displaystyle \frac{(3x - 2)}{(10x - 11)}\)

Correct answer:

\(\displaystyle \frac{(3x - 2)}{(10x - 11)}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Notice that as x increases, the function graphed appears to}\\&\text{level out, flattening towards a certain value. This value is}\\&\text{what is known as a horizontal asymptote. An asymptote is a value}\\&\text{that a function approaches, but never actually reaches. Think}\\&\text{of a horizontal asymptote as the limit of a function as x approaches}\\&\text{infinity. In such a case, as x approaches infinity, any constants}\\&\text{added or subtracted in the numerator and denominator become}\\&\text{irrelevant. What matters is the power of x in the denominator}\\&\text{and the numerator; if those are the same, then the coefficients}\\&\text{define the asymptote. We see that the function flattens towards:}\\&f(\infty)=0.3\\&\text{This matches the ratio of coefficients for the function: }\\&\frac{(3x - 2)}{(10x - 11)}\end{align*}\)

Example Question #5 : Asymptotic And Unbounded Behavior

Asymptoteplot

\(\displaystyle \begin{align*}&\text{Of the following functions, which most likely represents the graph above?}\end{align*}\)

Possible Answers:

\(\displaystyle -\frac{(19x + 9)}{(17x - 5)}\)

\(\displaystyle -\frac{(17x - 5)}{(19x + 9)}\)

\(\displaystyle \frac{(17x - 5)}{(19x + 9)}\)

\(\displaystyle \frac{(19x + 9)}{(17x - 5)}\)

Correct answer:

\(\displaystyle -\frac{(19x + 9)}{(17x - 5)}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Notice that as x increases, the function graphed appears to}\\&\text{level out, flattening towards a certain value. This value is}\\&\text{what is known as a horizontal asymptote. An asymptote is a value}\\&\text{that a function approaches, but never actually reaches. Think}\\&\text{of a horizontal asymptote as the limit of a function as x approaches}\\&\text{infinity. In such a case, as x approaches infinity, any constants}\\&\text{added or subtracted in the numerator and denominator become}\\&\text{irrelevant. What matters is the power of x in the denominator}\\&\text{and the numerator; if those are the same, then the coefficients}\\&\text{define the asymptote. We see that the function flattens towards:}\\&f(\infty)=-1.12\\&\text{This matches the ratio of coefficients for the function: }\\&-\frac{(19x + 9)}{(17x - 5)}\end{align*}\)

Example Question #1 : Identifying Asymptotes Graphically

Asymptoteplot

\(\displaystyle \begin{align*}&\text{Of the following functions, which most likely represents the graph above?}\end{align*}\)

Possible Answers:

\(\displaystyle -\frac{(15x + 4)}{(x - 13)}\)

\(\displaystyle -\frac{(x + 13)}{(15x - 4)}\)

\(\displaystyle -\frac{(x - 13)}{(15x + 4)}\)

\(\displaystyle -\frac{(15x - 4)}{(x + 13)}\)

Correct answer:

\(\displaystyle -\frac{(x - 13)}{(15x + 4)}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Observation of the graph shows that there’s a sharp increase}\\&\text{and decrease on either side of a particular x-value. This type}\\&\text{of behavior is observed when there’s a vertical asymptote. An}\\&\text{asymptote is a value that a function may approach, but will}\\&\text{never actually attain. In the case of vertical asymptotes, this}\\&\text{behavior occurs if the function approaches infinity for a given}\\&\text{x-value, often when a zero value appears in a denominator. Noting}\\&\text{this rule, the above function has a zero in the denominator}\\&\text{at a definite point centered approximately around:}\\&x=-0.3\\&\text{We find a zero denominator for the function: }\\&-\frac{(x - 13)}{(15x + 4)}\end{align*}\)

Example Question #1 : Identifying Asymptotes Graphically

Asymptoteplot

\(\displaystyle \begin{align*}&\text{Of the following functions, which most likely represents the graph above?}\end{align*}\)

Possible Answers:

\(\displaystyle \frac{(15x - 1)}{(9x - 11)}\)

\(\displaystyle \frac{(9x + 11)}{(15x + 1)}\)

\(\displaystyle \frac{(9x - 11)}{(15x - 1)}\)

\(\displaystyle \frac{(15x + 1)}{(9x + 11)}\)

Correct answer:

\(\displaystyle \frac{(9x - 11)}{(15x - 1)}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Observation of the graph shows that there’s a sharp increase}\\&\text{and decrease on either side of a particular x-value. This type}\\&\text{of behavior is observed when there’s a vertical asymptote. An}\\&\text{asymptote is a value that a function may approach, but will}\\&\text{never actually attain. In the case of vertical asymptotes, this}\\&\text{behavior occurs if the function approaches infinity for a given}\\&\text{x-value, often when a zero value appears in a denominator. Noting}\\&\text{this rule, the above function has a zero in the denominator}\\&\text{at a definite point centered approximately around:}\\&x=0.1\\&\text{We find a zero denominator for the function: }\\&\frac{(9x - 11)}{(15x - 1)}\end{align*}\)

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