AP Calculus AB : Derivative rules for sums, products, and quotients of functions

Study concepts, example questions & explanations for AP Calculus AB

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Example Questions

Example Question #422 : Derivatives

Find the derivative of \(\displaystyle y=5x^3e^x\)

Possible Answers:

\(\displaystyle 5x^2e^x(3+x)\)

none of these answers

\(\displaystyle 15x^2e^x\)

\(\displaystyle 15x^2e^x+5x^3\)

\(\displaystyle 15x^2e^x+5x^3xe\)

Correct answer:

\(\displaystyle 5x^2e^x(3+x)\)

Explanation:

So whenever you have two distinct functions that are multiplied by each other, you will be using the product rule. So when looking at a function, see if you can separate it into two. In this case, we can see there is the function:

\(\displaystyle 5x^3\) and the function \(\displaystyle e^x\).

So lets call those \(\displaystyle f(x) and g(x)\)

Then the product rule is that the derivative of \(\displaystyle f(x)g(x )\) is:

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

Then calculate to find:

\(\displaystyle f'(x)=15x^2\) and \(\displaystyle g'(x)=e^x\) to give an answer of:

\(\displaystyle f'(x)g(x)+f(x)g'(x)=15x^2e^x+5x^3e^x\)

which simplifies to:

\(\displaystyle 5x^2e^x(3+x)\)

Example Question #52 : Derivative Rules For Sums, Products, And Quotients Of Functions

Find the derivative of the following function:

\(\displaystyle f=2x^3+5x^2+x-4\)

Possible Answers:

\(\displaystyle f'=6x^2+11\)

\(\displaystyle f'=6x^2+10x+1\)

\(\displaystyle f'=6x^3+10x^2+x\)

\(\displaystyle f'=6x^2+10x+x-4\)

Correct answer:

\(\displaystyle f'=6x^2+10x+1\)

Explanation:

To find the derivative of the sum, we take the derivative of each term independently, then add them all up. Further, we use the rule

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

\(\displaystyle f'=\frac{\mathrm{d} }{\mathrm{d} x}(2x^3)+\frac{\mathrm{d} }{\mathrm{d} x}(5x^2)+\frac{\mathrm{d} }{\mathrm{d} x}(x)+\frac{\mathrm{d} }{\mathrm{d} x}(-4)\)

\(\displaystyle f'=6x^2+10x+1\)

Example Question #431 : Derivatives

Find the derivative of the following function

\(\displaystyle f=5x\cos(x)\)

Possible Answers:

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

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

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

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

Correct answer:

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

Explanation:

To find the derivative of the function, we must use the product rule, which is

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(f(x)*g(x))=f'(x)g(x)+f(x)g'(x)\)

Using the function from the problem statement, we get

\(\displaystyle f'=\frac{\mathrm{d} }{\mathrm{d} x}(5x)*(\cos(x))+\frac{\mathrm{d} }{\mathrm{d} x}(\cos(x))*5x\)

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

Example Question #432 : Derivatives

Find the derivative of the following function:

\(\displaystyle f=\frac{4x^3+\sin(x)}{\tan(x)}\)

Possible Answers:

\(\displaystyle f'=\frac{\tan(x)(12x^3+\cos(x))-(4x^3+\cos(x))(\sec^2(x))}{\tan^2(x)}\)

\(\displaystyle f'=\frac{\tan(x)(12x^2+\cos(x))-(4x^3+\sin(x))(\sec^2(x))}{\sec^2(x)}\)

\(\displaystyle f'=\frac{\tan(x)(12x^2+\cos(x))-(4x^3+\sin(x))(\sec^2(x))}{\tan^2(x)}\)

\(\displaystyle f'=\frac{\tan(x)(12x^2+\cos(x))+(4x^3+\sin(x))(\tan^2(x))}{\tan^2(x)}\)

Correct answer:

\(\displaystyle f'=\frac{\tan(x)(12x^2+\cos(x))-(4x^3+\sin(x))(\sec^2(x))}{\tan^2(x)}\)

Explanation:

To find the derivative of the function, we use the quotient rule, which is

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(\frac{f}{g})=\frac{gf'-fg'}{g^2}\), where \(\displaystyle f\) and \(\displaystyle g\) are any expression

Using the function from the problem statement, we get

\(\displaystyle f'=\frac{\tan(x)*\frac{\mathrm{d} }{\mathrm{d} x}(4x^3+\sin(x))-(4x^3+\sin(x))*\frac{\mathrm{d} }{\mathrm{d} x}(\tan(x))}{\tan^2(x)}\)

Taking the derivatives, we get

\(\displaystyle f'=\frac{\tan(x)(12x^2+\cos(x))-(4x^3+\sin(x))(\sec^2(x))}{\tan^2(x)}\)

Example Question #433 : Derivatives

Find the derivative of the function

\(\displaystyle f=12x^2+\sin(x)-100\)

Possible Answers:

\(\displaystyle 24x+\cos(x)\)

\(\displaystyle 24x^2-\cos(x)\)

\(\displaystyle 12x+\cos^2(x)\)

\(\displaystyle 24x-\cos(x)\)

Correct answer:

\(\displaystyle 24x+\cos(x)\)

Explanation:

To find the derivative of the sum, we take the derivative of each term independently, then add them all up. Further, we use the rule

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

\(\displaystyle f'=\frac{\mathrm{d} }{\mathrm{d} x}(12x^2)+\frac{\mathrm{d} }{\mathrm{d} x}(\sin(x))-\frac{\mathrm{d} }{\mathrm{d} x}(100)\)

\(\displaystyle f'=24x+\cos(x)\)

Example Question #51 : Derivative Rules For Sums, Products, And Quotients Of Functions

Find the derivative of the following function:

\(\displaystyle f=2x^2+5x-1\)

Possible Answers:

\(\displaystyle f'=4x+4\)

\(\displaystyle f'=4x+5\)

\(\displaystyle f'=4x^3+5x^2\)

\(\displaystyle f'=9x\)

Correct answer:

\(\displaystyle f'=4x+5\)

Explanation:

To find the derivative of the function, we take the derivative of each element in the function independently, then add them up.

Using \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}x^n=nx^{n-1}\), we solve

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(2x^2)+\frac{\mathrm{d} }{\mathrm{d} x}(5x)+\frac{\mathrm{d} }{\mathrm{d} x}(-1)=4x+5\)

Example Question #435 : Derivatives

Find the derivative of the following function:

\(\displaystyle f=2x^5\sin{x}\)

Possible Answers:

\(\displaystyle f'=10x^5\sin{x}+x^5\cos{x}\)

\(\displaystyle f'=10x^4\sin{x}-2x^5\cos{x}\)

\(\displaystyle f'=10x^4\sin{x}+2x^5\cos{x}\)

\(\displaystyle f'=10x^4\sin{x}+2x^5\sin{x}\)

Correct answer:

\(\displaystyle f'=10x^4\sin{x}+2x^5\cos{x}\)

Explanation:

To find the derivative of the function, we use the product rule, which is defined as

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(f*g)=(f'*g)+(f*g')\), where f and g are both functions.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(2x^5\sin{x})=\frac{\mathrm{d} }{\mathrm{d} x}(2x^5)*(\sin{x})+\frac{\mathrm{d} }{\mathrm{d} x}(\sin{x})*(2x^5)=10x^4\sin{x}+2x^5\cos{x}\)

Example Question #261 : Computation Of The Derivative

Find the derivative of the following function using the quotient rule:

\(\displaystyle f=\frac{e^x}{\tan{x}}\)

Possible Answers:

\(\displaystyle f'=\frac{e^x\tan{x}+e^x\sec^2{x}}{\tan^2{x}}\)

\(\displaystyle f'=\frac{e^x\tan{x}-e^x\sec^2{x}}{\tan^2{x}}\)

\(\displaystyle f'=\frac{e^x\tan{x}-e^x\sec^2{x}}{\tan{x}}\)

\(\displaystyle f'=\frac{xe^x\tan{x}-e^x\sec^2{x}}{\tan^2{x}}\)

Correct answer:

\(\displaystyle f'=\frac{e^x\tan{x}-e^x\sec^2{x}}{\tan^2{x}}\)

Explanation:

To find the derivative of the function using the quotient rule, we apply the following definition:

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(\frac{f}{g})=\frac{gf'-fg'}{g^2}\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(\frac{e^x}{\tan{x}})=\frac{\tan{x}*\frac{\mathrm{d} }{\mathrm{d} x}(e^x)-e^x*\frac{\mathrm{d} }{\mathrm{d} x}(\tan{x})}{\tan^2{x}}=\frac{e^x\tan{x}-e^x\sec^2{x}}{\tan^2{x}}\)

 

 

 

Example Question #52 : Derivative Rules For Sums, Products, And Quotients Of Functions

Find the derivative of the following function:

\(\displaystyle f=10x^3+5x^2-1\)

Possible Answers:

\(\displaystyle f'=30x^2+10x\)

\(\displaystyle f'=3x^2+x\)

\(\displaystyle f'=30x^3+10x^2\)

\(\displaystyle f'=30x^2+10x-1\)

Correct answer:

\(\displaystyle f'=30x^2+10x\)

Explanation:

To find the derivative of the function, we take the derivative of each element in the function independently, then add them up.

Using \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}x^n=nx^{n-1}\), we solve

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(10x^3)+\frac{\mathrm{d} }{\mathrm{d} x}(5x^2)+\frac{\mathrm{d} }{\mathrm{d} x}(-1)=30x^2+10x\)

Example Question #60 : Derivative Rules For Sums, Products, And Quotients Of Functions

Determine the second derivative of \(\displaystyle f(x)=ln(x^2-1)\)

Possible Answers:

\(\displaystyle f''(x)=\frac{2x^2-1}{x^4-2x^2}\)

\(\displaystyle f''(x)=\frac{x}{2x -1}\)

\(\displaystyle f''(x)=\frac{-2x^2-2}{x^4-2x^2+1}\)

\(\displaystyle f''(x)=\frac{2x^2-2}{x^3-x^2+1}\)

\(\displaystyle f''(x)=\frac{2x}{x^2-1}\)

Correct answer:

\(\displaystyle f''(x)=\frac{-2x^2-2}{x^4-2x^2+1}\)

Explanation:

Finding our second derivative requires two steps, we first must find the derivative then find the corresponding rate of change for that new equation.

\(\displaystyle f(x)=ln(x^2-1)\)

Here, the chain rule is used since our function is of the form \(\displaystyle [f(g(x))]dx=f'(x)g'(f(x))\)

\(\displaystyle f'(x)=\frac{2x}{x^2-1}\)

We now must use the quotient rule since our function is a rational function. We use the rule \(\displaystyle [\frac{f(x)}{g(x)}]dx=\frac{f'(x)g(x)-g'(x)f(x))}{(g(x))^2}\)

Therefore,

\(\displaystyle f''(x)=\frac{-2x^2-2}{x^4-2x^2+1}\)

 

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