Calculus 1 : Differential Functions

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #832 : Other Differential Functions

Find the first derivative of the following function:

\(\displaystyle f(x)=3xe^{x}+12\cos(x)\)

Possible Answers:

\(\displaystyle 3+3xe^x-12\sin(x)\)

\(\displaystyle 3e^x+3xe^x+12\sin(x)\)

\(\displaystyle 3e^x+3xe^x-12\sin(x)\)

\(\displaystyle 3e^x+3xe^x-\sin(x)\)

\(\displaystyle 3e^x+3x^2e^x-12\sin(x)\)

Correct answer:

\(\displaystyle 3e^x+3xe^x-12\sin(x)\)

Explanation:

The derivative of the function is equal to

\(\displaystyle f'(x)=3e^x+3xe^x-12\sin(x)\)

and was found using the following rules:

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} f(x)g(x)=f'(x)g(x)+f(x)g'(x)\), \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} x^n=nx^{n-1}\), \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} e^x=e^x\), \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} \cos(x)=-\sin(x)\)

Example Question #832 : How To Find Differential Functions

Find the derivative of the following function at x=1:

\(\displaystyle (f\circ g)(x)\)

where \(\displaystyle f(x)=2x^2\), \(\displaystyle g(x)=5x\)

Possible Answers:

\(\displaystyle 100\)

\(\displaystyle 0\)

\(\displaystyle 20\)

\(\displaystyle 50\)

Correct answer:

\(\displaystyle 100\)

Explanation:

To find the derivative of the composite function, we must rewrite the composition as \(\displaystyle f(g(x))\). Using the chain rule, the derivative of this function is equal to

\(\displaystyle f'(g(x)) \cdot g'(x)\).

For our function,

\(\displaystyle f'(x)=4x\) and \(\displaystyle g'(x)=5\). These derivatives were found using the following rule:

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

We now have all the pieces to use the chain rule formula, where we are evaluating the function at x=1:

\(\displaystyle g(1)=5\)

\(\displaystyle g'(1)=5\)

\(\displaystyle f'(g(1))=f'(5)=20\)

\(\displaystyle 20 \cdot 5=100\)

 

Example Question #834 : Other Differential Functions

Find the first derivative of the function:

\(\displaystyle f(x)= \frac{t^4-t^2}{e^t}\)

Possible Answers:

\(\displaystyle e^t(-t^4+4t^3+t^2-2t)\)

\(\displaystyle e^t(t^4+4t^3+t^2+2t)\)

\(\displaystyle e^t(2t-t^2)\)

\(\displaystyle \frac{-t^4+4t^3+t^2-2t}{e^{2t}}\)

Correct answer:

\(\displaystyle e^t(-t^4+4t^3+t^2-2t)\)

Explanation:

The derivative of the function is equal to

\(\displaystyle f'(x)=\frac{e^t(4t^3-2t)-e^t(t^4+t^2)}{e^{2t}}=e^t(-t^4+4t^3+t^2-2t)\)

and was found using the following rules:

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} \frac{f(x)}{g(x)}=\frac{g(x)f'(x)-f(x)g'(x)}{g(x)^2}\), \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} x^n=nx^{n-1}\), \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} e^x=e^x\)

Example Question #1021 : Differential Functions

Find the second derivative of the function:

\(\displaystyle f(x)=\cos(\sec(e^{10x^2}))\)

Possible Answers:

\(\displaystyle 1\)

\(\displaystyle 20xe^{10x^2}\sec(x)\tan(x)\)

 \(\displaystyle 20xe^{10x^2}\)

\(\displaystyle -20xe^{10x^2}\)

\(\displaystyle 0\)

Correct answer:

 \(\displaystyle 20xe^{10x^2}\)

Explanation:

Because \(\displaystyle \cos(x)\) and \(\displaystyle \sec(x)\) are inverses of each other, we can simplify the given function to

\(\displaystyle f(x)=e^{10x^2}\)

Taking the derivative of this, we get

\(\displaystyle f'(x)=20xe^{10x^2}\)

by using the following rules:

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} e^u=e^u\frac{\mathrm{du} }{\mathrm{d} x}\), \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x} x^n=nx^{n-1}\)

Example Question #832 : Other Differential Functions

Determine the slope of the line that is tangent to the function \(\displaystyle f(x)=sin(10x)\) at the point \(\displaystyle x=\pi\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle -1\)

\(\displaystyle -10\)

\(\displaystyle 10\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle -10\)

Explanation:

The slope of the tangent can be found by taking the derivative of the function and evaluating the value of the derivative at a point of interest.

We'll need to make use of the following derivative rule(s):

Trigonometric derivative: 

\(\displaystyle d[sin(u)]=cos(u)du\)

Note that u may represent large functions, and not just individual variables!

Taking the derivative of the function \(\displaystyle f(x)=sin(10x)\) at the point \(\displaystyle x=\pi\)

The slope of the tangent is

\(\displaystyle f'(x)=10cos(x)\)

\(\displaystyle f'(\pi)=10cos(\pi)=-10\)

 

Example Question #1021 : Differential Functions

Determine the slope of the line that is tangent to the function \(\displaystyle f(x)=sin(5\pi x^2)\) at the point \(\displaystyle x=2\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle 20\pi\)

\(\displaystyle -10\pi\)

\(\displaystyle -20\pi\)

\(\displaystyle 10\pi\)

Correct answer:

\(\displaystyle 20\pi\)

Explanation:

The slope of the tangent can be found by taking the derivative of the function and evaluating the value of the derivative at a point of interest.

We'll need to make use of the following derivative rule(s):

Trigonometric derivative: 

\(\displaystyle d[sin(u)]=cos(u)du\)

Note that u may represent large functions, and not just individual variables!

Taking the derivative of the function \(\displaystyle f(x)=sin(5\pi x^2)\) at the point \(\displaystyle x=2\)

The slope of the tangent is

\(\displaystyle f'(x)=10\pi x cos(5\pi x^2)\)

\(\displaystyle f'(2)=10\pi (2) cos(5\pi (2)^2)=20\pi\)

 

Example Question #837 : Other Differential Functions

Determine the slope of the line that is tangent to the function \(\displaystyle f(x)=sin^2(5x)\) at the point \(\displaystyle x=\pi\)

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle 0\)

\(\displaystyle -5\)

\(\displaystyle -10\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 0\)

Explanation:

The slope of the tangent can be found by taking the derivative of the function and evaluating the value of the derivative at a point of interest.

We'll need to make use of the following derivative rule(s):

Trigonometric derivative: 

\(\displaystyle d[sin(u)]=cos(u)du\)

Note that u may represent large functions, and not just individual variables!

Taking the derivative of the function \(\displaystyle f(x)=sin^2(5x)\) at the point \(\displaystyle x=\pi\)

The slope of the tangent is

\(\displaystyle f'(x)=10sin(5x)cos(5x)\)

\(\displaystyle f'(\pi)=10sin(5\pi)cos(5\pi)=0\)

 

Example Question #841 : Other Differential Functions

Determine the slope of the line that is tangent to the function \(\displaystyle f(x)=cos(4x)\) at the point \(\displaystyle x=\frac{\pi}{2}\)

Possible Answers:

\(\displaystyle -4\)

\(\displaystyle 4\)

\(\displaystyle 1\)

\(\displaystyle -1\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 0\)

Explanation:

The slope of the tangent can be found by taking the derivative of the function and evaluating the value of the derivative at a point of interest.

We'll need to make use of the following derivative rule(s):

Trigonometric derivative: 

\(\displaystyle d[cos(u)]=-sin(u)du\)

Note that u may represent large functions, and not just individual variables!

Taking the derivative of the function \(\displaystyle f(x)=cos(4x)\) at the point \(\displaystyle x=\frac{\pi}{2}\)

The slope of the tangent is

\(\displaystyle f'(x)=-4sin(4x)\)

\(\displaystyle f'(\frac{\pi}{2})=-4sin(4(\frac{\pi}{2}))=0\)

 

Example Question #1021 : Differential Functions

Determine the slope of the line that is tangent to the function \(\displaystyle f(x)=cos^2(\pi x^2)\) at the point \(\displaystyle x=\frac{1}{2}\)

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle \pi\)

\(\displaystyle -4\pi\)

\(\displaystyle -\pi\)

\(\displaystyle -2\pi\)

Correct answer:

\(\displaystyle -\pi\)

Explanation:

The slope of the tangent can be found by taking the derivative of the function and evaluating the value of the derivative at a point of interest.

We'll need to make use of the following derivative rule(s):

Trigonometric derivative: 

\(\displaystyle d[cos(u)]=-sin(u)du\)

Note that u may represent large functions, and not just individual variables!

Taking the derivative of the function \(\displaystyle f(x)=cos^2(\pi x^2)\) at the point \(\displaystyle x=\frac{1}{2}\)

The slope of the tangent is

\(\displaystyle f'(x)=-4\pi x sin(\pi x^2)cos(\pi x^2)\)

\(\displaystyle f'(\frac{1}{2})=-4\pi (\frac{1}{2}) sin(\pi (\frac{1}{2})^2)cos(\pi (\frac{1}{2})^2)=-\pi\)

 

Example Question #841 : How To Find Differential Functions

Determine the slope of the line that is tangent to the function \(\displaystyle f(x)=cos(sin(x))\) at the point \(\displaystyle x=3\pi\)

Possible Answers:

\(\displaystyle -1\)

\(\displaystyle 3\)

\(\displaystyle -3\)

\(\displaystyle 0\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 0\)

Explanation:

The slope of the tangent can be found by taking the derivative of the function and evaluating the value of the derivative at a point of interest.

We'll need to make use of the following derivative rule(s):

Trigonometric derivative: 

\(\displaystyle d[sin(u)]=cos(u)du\)

\(\displaystyle d[cos(u)]=-sin(u)du\)

Note that u may represent large functions, and not just individual variables!

Taking the derivative of the function \(\displaystyle f(x)=cos(sin(x))\) at the point \(\displaystyle x=3\pi\)

The slope of the tangent is

\(\displaystyle f'(x)=cos(x)sin(sin(x))\)

\(\displaystyle f'(3\pi)=cos(3\pi)sin(sin(3\pi))=0\)

 

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