High School Math : Finding Derivative of a Function

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : Derivative Defined As The Limit Of The Difference Quotient

What is the derivative of \(\displaystyle 2x^4+\frac{1}{2}x\)?

Possible Answers:

\(\displaystyle \frac{2}{5}x^5+\frac{1}{4}x^2+c\)

\(\displaystyle 4x+1\)

\(\displaystyle 5\)

\(\displaystyle 8x^{3}+\frac{1}{2}\)

\(\displaystyle 8x^2+\frac{1}{2}x\)

Correct answer:

\(\displaystyle 8x^{3}+\frac{1}{2}\)

Explanation:

To take the derivative of this equation, we can use the power rule. The power rule says that we lower the exponent of each variable by one and multiply that number by the original exponent.

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

Simplify.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(2x^4+\frac{1}{2}x)=(4*2x^{3})+(\frac{1}{2}x^{0})\)

Remember that anything to the zero power is equal to one.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(2x^4+\frac{1}{2}x)=(8x^{3})+(\frac{1}{2}*1)\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(2x^4+\frac{1}{2}x)=8x^{3}+\frac{1}{2}\)

Example Question #2 : Derivative Defined As The Limit Of The Difference Quotient

What is the derivative of \(\displaystyle 3x+12\)?

Possible Answers:

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

\(\displaystyle 15\)

\(\displaystyle 3x^2\)

\(\displaystyle 3\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle 3\)

Explanation:

To take the derivative of this equation, we can use the power rule. The power rule says that we lower the exponent of each variable by one and multiply that number by the original exponent.

We are going to treat \(\displaystyle 12\) as \(\displaystyle 12x^0\) since anything to the zero power is one.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(3x+12)=(3x^{1-1})+(0*12x^{0-1})\)

Notice that \(\displaystyle (0*12x^{0-1})=0\) since anything times zero is zero.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(3x+12)=(3x^{1-1})\)

Simplify.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(3x+12)=(3x^{0})\)

As stated before, anything to the zero power is one.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(3x+12)=3*1\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(3x+12)=3\)

Example Question #621 : Derivatives

What is the derivative of \(\displaystyle 5x^2+12x\)?

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle 10x+12\)

\(\displaystyle 2x+12\)

\(\displaystyle 2x+1\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 10x+12\)

Explanation:

To find the first derivative, we can use the power rule. We lower the exponent on all the variables by one and multiply by the original variable.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(5x^2+12x)=(2*5x^{2-1})+(1*12x^{1-1})\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(5x^2+12x)=(2*5x^{1})+(1*12x^{0})\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(5x^2+12x)=10x^1+12x^0\)

Anything to the zero power is one.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(5x^2+12x)=10x^1+12(1)\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(5x^2+12x)=10x+12\)

Example Question #1171 : Ap Calculus Ab

What is the derivative of \(\displaystyle -8x^2+15\)?

Possible Answers:

\(\displaystyle 16x\)

\(\displaystyle 16\)

\(\displaystyle 2x\)

\(\displaystyle -16x\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle -16x\)

Explanation:

To find the first derivative, we can use the power rule. We lower the exponent on all the variables by one and multiply by the original variable.

We're going to treat \(\displaystyle 15\) as \(\displaystyle 15x^0\) since anything to the zero power is one.

For this problem that would look like this:

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(-8x^2+15)=(2*-8x^{2-1})+(0*15x^{0-1})\)

Notice that \(\displaystyle (0*15x^{0-1})=0\) since anything times zero is zero.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(-8x^2+15)=(2*-8x^{1})\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(-8x^2+15)=-16x\)

Example Question #623 : Derivatives

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

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle \frac{1}{4}x^4+\frac{2}{3}x^3+5x+c\)

\(\displaystyle 3x^2+4x\)

\(\displaystyle 6x\)

\(\displaystyle 3x^2+4x+\frac{5}{x}\)

Correct answer:

\(\displaystyle 3x^2+4x\)

Explanation:

To find the first derivative, we can use the power rule. To do that, we lower the exponent on the variables by one and multiply by the original exponent.

We're going to treat \(\displaystyle 5\) as \(\displaystyle 5x^0\) since anything to the zero power is one.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(x^3+2x^2+5)=(3*x^{3-1})+(2*2x^{2-1})+(0*5x^{0-1})\)

Notice that \(\displaystyle (0*5x^{0-1}) =0\) since anything times zero is zero.

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

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

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

 

Example Question #11 : Finding Derivatives

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(4x+3)=?\)

Possible Answers:

\(\displaystyle 4\)

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

\(\displaystyle 7\)

\(\displaystyle 4x^2+3x+c\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle 4\)

Explanation:

To find the derivative of the problem, we can use the power rule. The power rule says to multiply the coefficient of the variable by the exponent of the variable and then lower the exponent value by one.

To make that work, we're going to treat \(\displaystyle 3\) as \(\displaystyle 3x^0\), since anything to the zero power is one.

This means that \(\displaystyle 4x+3\) is the same as \(\displaystyle 4x^1+3x^0\).

Now use the power rule:

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(4x^1+3x^0)=(1*4x^{1-1})+(0*3x^{0-1})\)

Anything times zero is zero.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(4x^1+3x^0)=(1*4x^{0})+0\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(4x^1+3x^0)=(1*4*1)\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(4x^1+3x^0)=4\)

Example Question #12 : Finding Derivatives

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

Possible Answers:

\(\displaystyle 12x^2+6\)

\(\displaystyle 6\)

\(\displaystyle 4x^{3}-6x\)

\(\displaystyle 4x^{3}-6x+\frac{8}{x}\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 4x^{3}-6x\)

Explanation:

To find the derivative of \(\displaystyle x^4-3x^2+8\), we can use the power rule.

The power rule states that we multiply each variable by its current exponent and then lower the exponent of each variable by one.

Since \(\displaystyle x^0=1\), we're going to treat \(\displaystyle 8\) as \(\displaystyle 8x^0\).

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}x^4-3x^2+8x^0=(4x^{4-1})-(2*3x^{2-1})+(0*8x^{0-1})\)

Anything times zero is zero, so our final term \(\displaystyle (0*8x^{0-1})=0\), regardless of the power of the exponent.

Simplify what we have.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}x^4-3x^2+8x^0=(4x^{3})-(6x^{1})\)

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}x^4-3x^2+8x^0=4x^{3}-6x\)

Our final solution, then, is \(\displaystyle 4x^3-6x\).

Example Question #31 : Derivatives

If \(\displaystyle f(x)=\frac{2}{3}x^3+7x^2-12x\), what is \(\displaystyle f'(x)\)?

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 4x+14\)

\(\displaystyle 2x^{2}+14x-12\)

\(\displaystyle \frac{1}{6}x^4+\frac{7}{3}x^3-6x^2+c\)

There is no \(\displaystyle f'(x)\) for this equation.

Correct answer:

\(\displaystyle 2x^{2}+14x-12\)

Explanation:

For this problem, we can use the power rule. The power rule states that we multiply each variable by its current exponent and then lower that exponent by one. 

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}f(x)=(3*\frac{2}{3}x^{3-1})+(2*7x^{2-1})-(1*12x^{1-1})\)

Simplify.

\(\displaystyle \frac{\mathrm{d} }{\mathrm{d} x}f(x)=(2x^{2})+(14x^{1})-(12x^{0})\)

Anything to the zero power is one, so \(\displaystyle 12x^0=12(1)=12\).

Therefore, \(\displaystyle f'(x)=2x^{2}+14x-12\).

Example Question #32 : Derivatives

Find the derivative of the following function:

\(\displaystyle f(x) = 6x^2+4x + 7\)

Possible Answers:

\(\displaystyle f'(x)= 12x^2 + 7\)

\(\displaystyle f'(x) = 6x\)

\(\displaystyle f'(x)= 12x + 7\)

\(\displaystyle f'(x)= 12x+4\)

\(\displaystyle f'(x)= 6x + 4\)

Correct answer:

\(\displaystyle f'(x)= 12x+4\)

Explanation:

We use the power rule on each term of the function.

The first term

\(\displaystyle 6x^2\)

becomes

\(\displaystyle 2 \times 6 x^2 = 12 x\).

The second term

\(\displaystyle 4x\)

becomes

\(\displaystyle 4\).

The final term, 7, is a constant, so its derivative is simply zero.

 

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