Calculus 2 : First and Second Derivatives of Functions

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #131 : First And Second Derivatives Of Functions

Find the derivative of the function \(\displaystyle f(x)=2x\cos(x)\)

Possible Answers:

\(\displaystyle 2\cos(x)-2x\sin(x)\)

\(\displaystyle 4x\cos(x)\)

\(\displaystyle 2x\cos(x)+1\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 2\cos(x)-2x\sin(x)\)

Explanation:

To solve, we use the product rule \(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}f(x)g(x)=f'(x)g(x)+f(x)g'(x)\). Applying, we get \(\displaystyle f'(x)= (2x)'\cos(x)+2x(\cos(x))'\). Taking the derivatives we get the correct solution \(\displaystyle 2\cos(x)-2x\sin(x)\)

Example Question #1457 : Calculus Ii

What is the second derivative of \(\displaystyle f(x)=5x^2-12x+4\)?

Possible Answers:

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

\(\displaystyle f{}''(x)=10\)

\(\displaystyle f{}''(x)=10x\)

\(\displaystyle f{}''(x)=x\)

\(\displaystyle f{}''(x)=10x-1\)

Correct answer:

\(\displaystyle f{}''(x)=10\)

Explanation:

To find the second derivative, you must first find the first derivative. Remember to multiply the exponent by the coefficient in front of the x term and then subtract one from the exponent:

\(\displaystyle f{}'(x)=10x-12\)

Now, take the derivative of the first derivative to find the second:

\(\displaystyle f{}''(x)=10\).

Example Question #1458 : Calculus Ii

What is the second derivative of \(\displaystyle f(x)=3x^3-8x^2+x-4?\)

Possible Answers:

\(\displaystyle f{}''(x)=18\)

\(\displaystyle f{}''(x)=18x^2-16x\)

\(\displaystyle f{}''(x)=18x\)

\(\displaystyle f{}''(x)=18x-16\)

\(\displaystyle f{}''(x)=\frac{18}{x}\)

Correct answer:

\(\displaystyle f{}''(x)=18x-16\)

Explanation:

First, find the first derivative. Remember to multiply the exponent by the coefficient in front of the x term and then subtract one from the exponent:

\(\displaystyle f{}'(x)=9x^2-16x+1\)

Now, take the second derivative:

\(\displaystyle f{}''(x)=18x-16\)

Example Question #1459 : Calculus Ii

What is the derivative of \(\displaystyle f(x)=2x^{\frac{5}{4}}\)?

Possible Answers:

\(\displaystyle f{}'(x)=\frac{5}{2}x^{\frac{1}{4}}\)

\(\displaystyle f{}'(x)=\frac{5}{2}x^{\frac{1}{4}}+C\)

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

\(\displaystyle f{}'(x)=\frac{3}{2}x^{\frac{1}{4}}\)

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

Correct answer:

\(\displaystyle f{}'(x)=\frac{5}{2}x^{\frac{1}{4}}\)

Explanation:

Remember that when differentiating, multiply the exponent by the coefficient in front of the x term and then subtract one from the exponent as well.

\(\displaystyle f{}'(x)=2(\frac{5}{4})x^{\frac{1}{4}}=\frac{10}{4}x^{\frac{1}{4}}\)

Simplify to get your answer.

\(\displaystyle f{}'(x)=\frac{5}{2}x^{\frac{1}{4}}\)

Example Question #132 : First And Second Derivatives Of Functions

What is the derivative of \(\displaystyle f(x)=-3t^2+4t-1?\)

Possible Answers:

\(\displaystyle f{}'(x)=6t+4\)

\(\displaystyle f{}'(x)=-6t+4t^2\)

\(\displaystyle f{}'(x)=-6t+4\)

\(\displaystyle f{}'(x)=-6t-4\)

\(\displaystyle f{}'(x)=-6t\)

Correct answer:

\(\displaystyle f{}'(x)=-6t+4\)

Explanation:

To take the derivative, remember to multiply the exponent by the coefficient in front of the x term:

\(\displaystyle f{}'(x)=-6t+4\)

Example Question #333 : Derivatives

What is the second derivative of \(\displaystyle f(x)=4x^3-2x+6\)?

Possible Answers:

\(\displaystyle f{}''(x)=24\)

\(\displaystyle f{}''(x)=4x\)

\(\displaystyle f{}''(x)=24x\)

\(\displaystyle f{}''(x)=24x+C\)

\(\displaystyle f{}''(x)=24x+2\)

Correct answer:

\(\displaystyle f{}''(x)=24x\)

Explanation:

Before you can take the second derivative, you must take the first derivative. Remember to multiply the exponent by the coefficient in front of the x term and then subtract one from the exponent:

\(\displaystyle f{}'(x)=12x^2-2\)

Now, take the derivative of this to find the second derivative:

\(\displaystyle f{}''(x)=24x\)

 

Example Question #1461 : Calculus Ii

What is the derivative of \(\displaystyle f(x)=5x^3-2x^2+4x?\)

Possible Answers:

\(\displaystyle f{}'(x)=15x^2-4x\)

\(\displaystyle f{}'(x)=15x^2-4x+4\)

\(\displaystyle f{}'(x)=15x^2-4x-4\)

\(\displaystyle f{}'(x)=15x^2+2x+4\)

\(\displaystyle f{}'(x)=-15x^2-4x+4\)

Correct answer:

\(\displaystyle f{}'(x)=15x^2-4x+4\)

Explanation:

To take the derivative, remember to multiply the exponent by the coefficient and then subtract one from the exponent:

\(\displaystyle f{}'(x)=15x^2-4x+4\)

Example Question #335 : Derivatives

What is the derivative of \(\displaystyle f(x)=9x^{\frac{2}{3}}-4x^2+x\)?

Possible Answers:

\(\displaystyle f{}'(x)=\frac{6}{x^{\frac{1}{3}}}-8x-1\)

\(\displaystyle f{}'(x)=\frac{6}{x^{\frac{1}{3}}}-8x\)

\(\displaystyle f{}'(x)=\frac{6}{x^{\frac{1}{3}}}-8x+1\)

\(\displaystyle f{}'(x)=\frac{6}{x^{\frac{2}{3}}}-8x+1\)

\(\displaystyle f{}'(x)=\frac{6}{x^{\frac{1}{3}}}-2x+1\)

Correct answer:

\(\displaystyle f{}'(x)=\frac{6}{x^{\frac{1}{3}}}-8x+1\)

Explanation:

Remember that when taking the derivative, multiply the exponent by the coefficient and then subtract one from the exponent:

\(\displaystyle f{}'(x)=6x^{\frac{-1}{3}}-8x+1\)

Simplify so you don't have a negative exponent:

\(\displaystyle f{}'(x)=\frac{6}{x^{\frac{1}{3}}}-8x+1\)

Example Question #1462 : Calculus Ii

Find the derivative of the given function

\(\displaystyle f(x)=x^x\)

Possible Answers:

\(\displaystyle x^x(1+\ln(\ln x))\)

\(\displaystyle x^x(1+\ln x)\)

\(\displaystyle x^{x-1}\ln(x-1)\)

\(\displaystyle x^x\ln(1+\ln x)\)

Correct answer:

\(\displaystyle x^x(1+\ln x)\)

Explanation:

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Example Question #337 : Derivatives

Find the first derivative of the following function: \(\displaystyle y=lnxcos(e^{x})\)

Possible Answers:

\(\displaystyle \frac{\mathrm{dy} }{\mathrm{d} x}=lnxsinxe^{x}\)

\(\displaystyle \frac{\mathrm{dy} }{\mathrm{d} x}=\frac{cos(e^{x})}{x}-e^{x}lnxsin(e^{x})\)

\(\displaystyle \frac{\mathrm{dy} }{\mathrm{d} x}=lnxcos(e^{x})+\frac{cosx}{x}\)

\(\displaystyle \frac{\mathrm{dy} }{\mathrm{d} x}=\frac{sin(e^{x})}{x}-e^{x}lnxsin(e^{x})\)

Correct answer:

\(\displaystyle \frac{\mathrm{dy} }{\mathrm{d} x}=\frac{cos(e^{x})}{x}-e^{x}lnxsin(e^{x})\)

Explanation:

To solve this problem, we use a combination of the product and chain rules. First, we use the product rule, which looks like this:

\(\displaystyle \frac{\mathrm{dy} }{\mathrm{d} x}=lnx\frac{\mathrm{d} }{\mathrm{d} x}cos(e^{x})+\frac{\mathrm{d} }{\mathrm{d} x}lnxcos(e^{x})\), which simplifies to:

 

\(\displaystyle \frac{dy}{dx}=lnx\frac{d}{dx}cos(e^{x})+\frac{cos(e^{x})}{x}\). We need to use the chain rule to find the derivative of \(\displaystyle cos(e^{x})\), which looks like this:

\(\displaystyle \frac{d}{dx}cos(e^{x})=-sin(e^{x})e^{x}\). Plugging this back into our equation above, we get:

\(\displaystyle \frac{dy}{dx}=-lnxsin(e^{x})e^{x}+\frac{cos(e^{x})}{x}\), which simplifies to:

\(\displaystyle \frac{dy}{dx}=\frac{cos(e^{x})}{x}-e^{x}lnxsin(e^{x})\)

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