Calculus 2 : Parametric

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #121 : Parametric, Polar, And Vector

Solve for \displaystyle \frac{dy}{dx} if \displaystyle x=9t+1 and \displaystyle y=4t+10.

Possible Answers:

None of the above

\displaystyle \frac{9}{4}

\displaystyle -\frac{4}{9}

\displaystyle -\frac{9}{4}

\displaystyle \frac{4}{9}

Correct answer:

\displaystyle \frac{4}{9}

Explanation:

We can determine that \displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}  since the \displaystyle dt terms will cancel out in the division process.

Since \displaystyle x=9t+1 and \displaystyle y=4t+10, we can use the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0 to derive 

\displaystyle \frac{dx}{dt}=(1)9t^{1-1}+(0)1=9 and \displaystyle \frac{dy}{dt}=(1)4t^{1-1}+(0)10=4  .

Thus:

.

Example Question #121 : Parametric, Polar, And Vector

What is \displaystyle \frac{dy}{dx} when \displaystyle x=2t+13 and \displaystyle y=4t+17?

Possible Answers:

\displaystyle -2

\displaystyle \frac{1}{2}

\displaystyle -\frac{1}{2}

None of the above

\displaystyle 2

Correct answer:

\displaystyle 2

Explanation:

We can first recognize that 

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}} 

since \displaystyle dt cancels out when we divide.

Then,  given \displaystyle x=2t+13 and \displaystyle y=4t+17 and using the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0,

we can determine that 

\displaystyle \frac{dy}{dt}=(1)4t^{1-1}+(0)17=4 and \displaystyle \frac{dx}{dt}=(1)2t^{1-1}+(0)13=2.

Therefore, 

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}=\frac{4}{2}=2.

Example Question #122 : Parametric, Polar, And Vector

What is \displaystyle \frac{dy}{dx} when \displaystyle x=-t+12 and \displaystyle y=\frac{8}{t}?

Possible Answers:

\displaystyle \frac{t^{2}}{8}

\displaystyle -\frac{8}{t^{2}}

\displaystyle \frac{8}{t^{2}}

None of the above

\displaystyle -\frac{t^{2}}{8}

Correct answer:

\displaystyle \frac{8}{t^{2}}

Explanation:

We can first recognize that 

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}} 

since \displaystyle dt cancels out when we divide.

Then,  given \displaystyle x=-t+12 and \displaystyle y=\frac{8}{t} or \displaystyle y=8t^{-1} and using the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0,

we can determine that 

\displaystyle \frac{dy}{dt}=(-1)8t^{-1-1}=-\frac{8}{t^{2}} and \displaystyle \frac{dx}{dt}=(1)(-1)t^{1-1}+(0)12=-1.

Therefore, 

\displaystyle \frac{dy}{dx}=\frac{-\frac{8}{t^{2}}}{-1}=\frac{8}{t^{2}}.

Example Question #123 : Parametric, Polar, And Vector

What is \displaystyle \frac{dy}{dx} when \displaystyle x=-6t+10 and \displaystyle y=7t-2?

Possible Answers:

None of the above

\displaystyle \frac{7}{6}

\displaystyle -\frac{6}{7}

\displaystyle -\frac{7}{6}

\displaystyle \frac{6}{7}

Correct answer:

\displaystyle -\frac{7}{6}

Explanation:

We can first recognize that

 \displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}} 

since \displaystyle dt cancels out when we divide.

Then,  given \displaystyle x=-6t+10 and \displaystyle y=7t-2 and using the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0,

we can determine that 

\displaystyle \frac{dy}{dt}=(1)7t^{1-1}-(0)2=7 and \displaystyle \frac{dx}{dt}=(1)(-6)t^{1-1}+(0)10=-6.

Therefore, 

\displaystyle \frac{dy}{dx}=\frac{7}{-6}=-\frac{7}{6}..

Example Question #122 : Parametric, Polar, And Vector

Find the derivative of the curve defined by the parametric equations.

\displaystyle x(t)=3sin(t)

\displaystyle y(t)=t^2+4t

Possible Answers:

\displaystyle \frac{dy}{dx}=-\frac{2t+4}{3sin(t)cos(t)}

\displaystyle \frac{dy}{dx}=3cos(t)+2t+4

\displaystyle \frac{dy}{dx}=\frac{6t^2cos(t)+10tcos(t)-4cos(t)}{9cos^2(t)}

\displaystyle \frac{dy}{dx}=\frac{2t+4}{3cos(t)}

Correct answer:

\displaystyle \frac{dy}{dx}=\frac{2t+4}{3cos(t)}

Explanation:

The first derivative of a parametrically defined curve is found by computing

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}.

We need to find the derivatives of y(t) and x(t) separately, and then find the quotient of the derivatives.

You will need to know that 

\displaystyle \frac{d}{dt}sin(t)=cos(t) and that \displaystyle \frac{d}{dt}t^n=nt^{n-1}.

\displaystyle x'(t)=\frac{dx}{dt}=3cos(t)

\displaystyle y'(t)=\frac{dy}{dt}=2t+4

Thus,

 \displaystyle \frac{dy}{dx}=\frac{2t+4}{3cos(t)}

Example Question #631 : Calculus Ii

Find the derivative of the following parametric function:

\displaystyle x=t^3+2t^2+4t, y=2t

Possible Answers:

\displaystyle \frac{2}{3t^2+4t+4}

\displaystyle 3t^2+4t+4

\displaystyle \frac{3t^2+4t+4}{2}

\displaystyle 2

Correct answer:

\displaystyle \frac{2}{3t^2+4t+4}

Explanation:

The derivative of a parametric equation is given by the following equation:

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}

The derivative of the equation for \displaystyle y is

\displaystyle \frac{dy}{dt}=2

and the derivative of the equation for \displaystyle x is

\displaystyle \frac{dx}{dt}=3t^2+4t+4

The derivatives were found using the following rule:

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

 

 

Example Question #124 : Parametric, Polar, And Vector

Find the derivative of the following parametric function:

\displaystyle x=3t+5\displaystyle y=te^t+\cos^2(t)

Possible Answers:

\displaystyle \frac{e^t-2\cos(t)\sin(t)}{3}

\displaystyle \frac{e^t+te^t+2\cos(t)\sin(t)}{3}

\displaystyle \frac{e^t+te^t-2\cos(t)\sin(t)}{3}

\displaystyle \frac{2\cos(t)\sin(t)}{3}

Correct answer:

\displaystyle \frac{e^t+te^t-2\cos(t)\sin(t)}{3}

Explanation:

The derivative of a parametric function is given by

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}

So, we must find the derivative of the functions with respect to t:

\displaystyle y'=e^t+te^t-2\cos(t)\sin(t)\displaystyle x'=3

The derivatives were found using the following rules:

\displaystyle \frac{d}{dx}(x^n)=nx^{n-1}\displaystyle \frac{d}{dx}(e^x)=e^x \displaystyle \frac{d}{dx}\cos(t)=-\sin(t)\displaystyle \frac{d}{dx}f(g(x))=f'(g(x))\cdot g'(x)

Simply divide the derivatives to get your answer. 

Example Question #125 : Parametric, Polar, And Vector

What is \displaystyle \frac{dy}{dx} 

if \displaystyle x=10t-3 and \displaystyle y=2t+9?

Possible Answers:

None of the above

\displaystyle -\frac{1}{5}

\displaystyle \frac{1}{5}

\displaystyle 5

\displaystyle -5

Correct answer:

\displaystyle \frac{1}{5}

Explanation:

We can first recognize that

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}} 

since \displaystyle dt  cancels out when we divide.

Then, given  \displaystyle x=10t-3 and \displaystyle y=2t+9 and using the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0, we can determine that 

\displaystyle \frac{dx}{dt}=(1)10t^{1-1}-(0)3=10 and 

\displaystyle \frac{dy}{dt}=(1)2t^{1-1}+(0)9=2.

Therefore, 

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}=\frac{2}{10}=\frac{1}{5}.

Example Question #126 : Parametric, Polar, And Vector

What is \displaystyle \frac{dy}{dx} 

if \displaystyle x=3t+2 and \displaystyle y=9t-5?

Possible Answers:

None of the above

\displaystyle \frac{1}{3}

\displaystyle 3

\displaystyle -\frac{1}{3}

\displaystyle -3

Correct answer:

\displaystyle 3

Explanation:

We can first recognize that 

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}} 

since \displaystyle dt  cancels out when we divide.

Then, given \displaystyle x=3t+2 and \displaystyle y=9t-5 and using the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0, we can determine that 

\displaystyle \frac{dx}{dt}=(1)3t^{1-1}+(0)2=3 and 

\displaystyle \frac{dy}{dt}=(1)9t^{1-1}-(0)5=9.

Therefore,

 \displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}=\frac{9}{3}=3.

Example Question #127 : Parametric, Polar, And Vector

What is \displaystyle \frac{dy}{dx} 

if \displaystyle x=5t-1 and \displaystyle y=t+5?

Possible Answers:

\displaystyle -5

\displaystyle \frac{1}{5}

\displaystyle 5

None of the above

\displaystyle -\frac{1}{5}

Correct answer:

\displaystyle \frac{1}{5}

Explanation:

We can first recognize that

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}} 

since \displaystyle dt  cancels out when we divide.

Then, given \displaystyle x=5t-1 and \displaystyle y=t+5 and using the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0, we can determine that

\displaystyle \frac{dx}{dt}=(1)5t^{1-1}-(0)1=5  and

\displaystyle \frac{dy}{dt}=(1)t^{1-1}+(0)5=1 .

Therefore, 

\displaystyle \frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}=\frac{1}{5}

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