Calculus 1 : Functions

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #1 : Approximation Of Rate

Find the average rate of change for \(\displaystyle x^2+x+1\) over the interval \(\displaystyle x=[0, 5]\).

Possible Answers:

\(\displaystyle 31/5\)

\(\displaystyle 1\)

\(\displaystyle 6\)

\(\displaystyle 31\)

Correct answer:

\(\displaystyle 6\)

Explanation:

The rate of change of a function is the amount it changes over a given amount of time.

In mathematical terms, this can be written as

\(\displaystyle r=\frac{\Delta y}{\Delta x}\)

we plug in our values:

\(\displaystyle \frac{5^2+5+1-0^2-0-1}{5-0} = \frac{30}{5}=6\)

Note that this is only an average because quadratic functions change at different rates depending on where you are in the function's domain.

Example Question #1 : How To Find Approximation Of Rate

Let \(\displaystyle f(x) = ln(e^{x}-sin(\pi -\pi x))\). Use linear approximation to estimate \(\displaystyle f(\frac{3}{2})\).

Possible Answers:

\(\displaystyle 2-\frac{\pi }{e^{3/2}}\)

\(\displaystyle \frac{3}{2}\)

\(\displaystyle \frac{\pi }{e^{3/2}}\)

\(\displaystyle 1-\frac{\pi }{e^{3/2}}\)

Correct answer:

\(\displaystyle 2-\frac{\pi }{e^{3/2}}\)

Explanation:

Note that:

 

\(\displaystyle f(1)= ln(e-sin(0))= lne =1\)

Therefore, for values relatively close  to 1, we can use the formula for dy (the differential form of the derivative) to estimate f at close values.

 

\(\displaystyle dy= \frac{e^{x}+\pi cos(\pi -\pi x)}{e^{x}-sin(\pi -\pi x)}dx\)  From log derivative with chain rule.

 

Since \(\displaystyle \frac{3}{2}\) lies \(\displaystyle \frac{1}{2}\) to the right of \(\displaystyle 1\), \(\displaystyle dx = \frac{1}{2}\) and \(\displaystyle x=1\) for the estimation, so:

 

\(\displaystyle dy = \frac{e^{3/2}+\pi cos(-\pi )}{e^{3/2}} = 1-\frac{\pi }{e^{3/2}}\)

 

So then:

\(\displaystyle f(3/2) \approx1+1-\frac{\pi }{e^{3/2}} = 2-\frac{\pi }{e^{3/2}}\)

Example Question #3 : How To Find Approximation Of Rate

Using \(\displaystyle (1+x)^{k}\approx1+kx\), approximate the value of \(\displaystyle (0.985)^{50}.\)

Possible Answers:

\(\displaystyle 0.75\)

\(\displaystyle 1.0\)

\(\displaystyle 1.25\)

\(\displaystyle 1.75\)

\(\displaystyle 0.25\)

Correct answer:

\(\displaystyle 0.25\)

Explanation:

First, we need to rearrange the given to match the approximation formula.  \(\displaystyle 0.985 = 1-0.015.\)  Therefore, \(\displaystyle (0.985)^{50}=(1-0.015)^{50}=1-50(0.015)=0.25.\textup{}\)

 

Example Question #4 : How To Find Approximation Of Rate

A cube is diminishing in size. What is the ratio of the rate of loss of the cube's volume to the rate of loss of its sides when its sides have length \(\displaystyle \frac{7}{30}\)?

Possible Answers:

\(\displaystyle \frac{7}{300}\)

\(\displaystyle \frac{49}{300}\)

\(\displaystyle \frac{49}{900}\)

\(\displaystyle \frac{7}{900}\)

\(\displaystyle \frac{49}{2700}\)

Correct answer:

\(\displaystyle \frac{49}{300}\)

Explanation:

Begin by writing the equations for a cube's dimensions. Namely its volume in terms of the length of its sides:

\(\displaystyle V=s^3\)

The rates of change of the volume can be found by taking the derivative of each side of the equation with respect to time:

\(\displaystyle \frac{dV}{dt}=3s^2\frac{ds}{dt}\)

Now, knowing the length of the sides, simply divide to find the ratio between the rate of change of the volume and sides:

\(\displaystyle 3s^2\frac{ds}{dt}=(\phi)\frac{ds}{dt}\)

\(\displaystyle \phi=3s^2\)

\(\displaystyle \phi =3(\frac{7}{30})^2=\frac{49}{300}\)

Example Question #5 : How To Find Approximation Of Rate

A cube is diminishing in size. What is the ratio of the rate of loss of the cube's volume to the rate of loss of its sides when its sides have length \(\displaystyle \frac{13}{15}\)?

Possible Answers:

\(\displaystyle \frac{169}{75}\)

\(\displaystyle \frac{13}{225}\)

\(\displaystyle \frac{13}{75}\)

\(\displaystyle \frac{169}{225}\)

\(\displaystyle \frac{169}{675}\)

Correct answer:

\(\displaystyle \frac{169}{75}\)

Explanation:

Begin by writing the equations for a cube's dimensions. Namely its volume in terms of the length of its sides:

\(\displaystyle V=s^3\)

The rates of change of the volume can be found by taking the derivative of each side of the equation with respect to time:

\(\displaystyle \frac{dV}{dt}=3s^2\frac{ds}{dt}\)

Now, knowing the length of the sides, simply divide to find the ratio between the rate of change of the volume and sides:

\(\displaystyle 3s^2\frac{ds}{dt}=(\phi)\frac{ds}{dt}\)

\(\displaystyle \phi=3s^2\)

\(\displaystyle \phi =3(\frac{13}{15})^2=\frac{169}{75}\)

Example Question #6 : How To Find Approximation Of Rate

A cube is diminishing in size. What is the ratio of the rate of loss of the cube's volume to the rate of loss of its sides when its sides have length \(\displaystyle \frac{1}{30}\)?

Possible Answers:

\(\displaystyle \frac{1}{900}\)

\(\displaystyle \frac{1}{2700}\)

\(\displaystyle \frac{1}{90}\)

\(\displaystyle \frac{1}{810}\)

\(\displaystyle \frac{1}{300}\)

Correct answer:

\(\displaystyle \frac{1}{300}\)

Explanation:

Begin by writing the equations for a cube's dimensions. Namely its volume in terms of the length of its sides:

\(\displaystyle V=s^3\)

The rates of change of the volume can be found by taking the derivative of each side of the equation with respect to time:

\(\displaystyle \frac{dV}{dt}=3s^2\frac{ds}{dt}\)

Now, knowing the length of the sides, simply divide to find the ratio between the rate of change of the volume and sides:

\(\displaystyle 3s^2\frac{ds}{dt}=(\phi)\frac{ds}{dt}\)

\(\displaystyle \phi=3s^2\)

\(\displaystyle \phi =3(\frac{1}{30})^2=\frac{1}{300}\)

Example Question #1 : How To Find Differentiable Of Rate

For the relation \(\displaystyle \small x^2y+2x-y^2=x\), compute \(\displaystyle \small y'\) using implicit differentiation. 

Possible Answers:

\(\displaystyle \small \small \small \small y'=-\frac{2x+1}{x^2-2y}\)

\(\displaystyle \small \small \small \small y'=-\frac{2xy+1}{y(x^2-2y)}\)

\(\displaystyle \small \small \small \small y'=-\frac{2xy+1}{x^2-2y}\)

\(\displaystyle \small \small \small \small y'=\frac{2xy+1}{x^2-2y}\)

Correct answer:

\(\displaystyle \small \small \small \small y'=-\frac{2xy+1}{x^2-2y}\)

Explanation:

Computing \(\displaystyle \small y'\) of the relation \(\displaystyle \small x^2y+2x-y^2=x\) can be done through implicit differentiation:

\(\displaystyle \small \small \frac{d}{dx}(x^2y+2x-y^2)=\frac{d}{dx}x\)

\(\displaystyle \small \small \implies 2xy+x^2y'+2-2yy'=1\)

Now we isolate the \(\displaystyle \small y'\):

\(\displaystyle \small \small \small \iff x^2y'-2yy'=1-2-2xy=-2xy-1\)

\(\displaystyle \small \iff y'(x^2-2y)=-(2xy+1)\)

\(\displaystyle \small \small \implies y'=-\frac{2xy+1}{x^2-2y}\)

Example Question #82 : Rate

In chemistry, rate of reaction is related directly to rate constant \(\displaystyle k\)

\(\displaystyle \frac{dC}{dt}=k\), where \(\displaystyle C\) is the initial concentration

Give the concentration of a mixture with rate constant \(\displaystyle k=\frac{3}{sec}\) and initial concentration \(\displaystyle C(0)=40M\), \(\displaystyle 10\) seconds after the reaction began.  

Possible Answers:

\(\displaystyle 70M\)

\(\displaystyle 40e^{(-30)}\)

\(\displaystyle 30e^{(-40)}\)

\(\displaystyle 30M\)

Correct answer:

\(\displaystyle 70M\)

Explanation:

This is a simple problem of integration. To find the formula for concentration from the formula of concentration rates, you simply take the integral of both sides of the rate equation with respect to time. 

\(\displaystyle \int \frac{dC}{dt} dt=\int (k)dt\)

Therefore, the concentration function is given by

\(\displaystyle C=kt+C_0\), where \(\displaystyle C_0\) is the initial concentration. 

Plugging in our values,

\(\displaystyle C=3*10+40= 70M\)

Example Question #1 : How To Find Differentiable Of Rate

\(\displaystyle x\) and \(\displaystyle y\) are related by the function \(\displaystyle y=3x^{4}-x+5\).  Find \(\displaystyle \frac{dy}{dt}\) at \(\displaystyle t=2\) if \(\displaystyle x=1\) and  \(\displaystyle \frac{dx}{dt}=6\) at \(\displaystyle t=2\).

Possible Answers:

\(\displaystyle \frac{dy}{dt}=6\)

\(\displaystyle \frac{dy}{dt}=60\)

\(\displaystyle \frac{dy}{dt}=12\)

\(\displaystyle \frac{dy}{dt}=73\)

\(\displaystyle \frac{dy}{dt}=66\)

Correct answer:

\(\displaystyle \frac{dy}{dt}=66\)

Explanation:

We will use the chain and power rules to differentiate both sides of this equation.

Power Rule: 

\(\displaystyle \frac{d}{dx}x^n=nx^{n-1}\)

Chain Rule:

\(\displaystyle \frac{d}{dx}f(g(x))=f'(g(x))\cdot g'(x)\).

Applying the above rules to our function we find the following derivative.

\(\displaystyle \frac{dy}{dt}=\frac{d}{dt}[3x^{4}-x+5]\)

\(\displaystyle \frac{dy}{dt}=12x^{3}\frac{dx}{dt}-1\frac{dx}{dt}\)

at \(\displaystyle t=2\)\(\displaystyle \frac{dx}{dt}=6\) and \(\displaystyle x=1\).

Therefore at \(\displaystyle t=2\)

\(\displaystyle \frac{dy}{dt}=12(1)^{3}(6)-1(6)=72-6=66\)

 

Example Question #82 : Rate

Let \(\displaystyle y = x^{xlnx-e}.\) Use logarithmic differentiation to find \(\displaystyle y'(e)\).

Possible Answers:

\(\displaystyle e\)

\(\displaystyle 2e\)

\(\displaystyle 2\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 2\)

Explanation:

The form of log differentiation after first "logging" both sides, then taking the derivative is as follows:

 

\(\displaystyle \frac{1}{y}y' = \frac{d}{dx}(lnf(x))\)    which implies

 

\(\displaystyle y' = f(x)\frac{d}{dx}(lnf(x))\)

 

So:

 

\(\displaystyle y'(e)=e^{elne-e}(ln^{2}e+2lne-\frac{e}{e})= 1(1+2-1)= 2\)

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