Calculus 2 : Derivative at a Point

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #11 : Derivative At A Point

Given the function \(\displaystyle f(x)=5x^{2}+9x-12\), what is the slope at the point \(\displaystyle (-1,3)\)?

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle 2\)

\(\displaystyle -2\)

\(\displaystyle 1\)

\(\displaystyle -1\)

Correct answer:

\(\displaystyle -1\)

Explanation:

As slope is defined as the derivative of a given function at a given point, we will need to take the derivative of \(\displaystyle f(x)=5x^{2}+9x-12\) and substitute in the \(\displaystyle x\)-value of the point \(\displaystyle (-1,3)\)

Using the Power Rule \(\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}\) for all \(\displaystyle n\neq0\)\(\displaystyle f'(x)=(2)5x^{2-1}+(1)9x^{1-1}-(0)12=10x+9\), Subbing in \(\displaystyle x=-1\), we get \(\displaystyle f'(-1)=10(-1)+9=-10+9=-1\).

Example Question #12 : Derivative At A Point

Given the function \(\displaystyle f(x)=x^{2}-7x-6\), what is the slope at the point \(\displaystyle (2,9)\)?

Possible Answers:

\(\displaystyle -3\)

\(\displaystyle -1\)

\(\displaystyle -5\)

\(\displaystyle -4\)

\(\displaystyle -2\)

Correct answer:

\(\displaystyle -3\)

Explanation:

As slope is defined as the derivative of a given function at a given point, we will need to take the derivative of \(\displaystyle f(x)=x^{2}-7x-6\) and substitute in the \(\displaystyle x\)-value of the point \(\displaystyle (2,9)\)

Using the Power Rule \(\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}\) for all \(\displaystyle n\neq0\)

\(\displaystyle f'(x)=(2)x^{2-1}-(1)7x^{1-1}-(0)6=2x-7\).

Swapping in \(\displaystyle x=2\), we get \(\displaystyle f'(2)=2(2)-7=4-7=-3\).

Example Question #13 : Derivative At A Point

Given \(\displaystyle f(x)=7x^{2}-2x+9\), find the value of \(\displaystyle f'(x)\) at the point \(\displaystyle (2,5)\)

Possible Answers:

\(\displaystyle 26\)

\(\displaystyle 25\)

\(\displaystyle 27\)

\(\displaystyle 28\)

\(\displaystyle 24\)

Correct answer:

\(\displaystyle 26\)

Explanation:

Given the function \(\displaystyle f(x)=7x^{2}-2x+9\), we can use the Power Rule

\(\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}\) for all \(\displaystyle n\neq0\) to find its derivative:

\(\displaystyle f'(x)=(2)7x^{2-1}-(1)2x^{1-1}+(0)9=14x-2\).

Plugging in the \(\displaystyle x\)-value of the point \(\displaystyle (2,5)\) into \(\displaystyle f'(x)\), we get 

\(\displaystyle f'(2)=14(2)-2=28-2=26\).

 

Example Question #51 : Derivatives

Given \(\displaystyle f(x)=5x^{2}+6x-12\), find the value of \(\displaystyle f'(x)\) at the point \(\displaystyle (-1,-1)\)

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle -4\)

\(\displaystyle 10\)

\(\displaystyle 6\)

\(\displaystyle -6\)

Correct answer:

\(\displaystyle -4\)

Explanation:

Given the function \(\displaystyle f(x)=5x^{2}+6x-12\), we can use the Power Rule

\(\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}\) for all \(\displaystyle n\neq0\) to find its derivative:

\(\displaystyle f'(x)=(2)5x^{2-1}+(1)6x^{1-1}-(0)12=10x+6\).

Plugging in the \(\displaystyle x\)-value of the point \(\displaystyle (-1,-1)\) into \(\displaystyle f'(x)\), we get 

\(\displaystyle f'(-1)=10(-1)+6=-10+6=-4\).

Example Question #52 : Derivatives

Given \(\displaystyle f(x)=10x^{2}-9x+1\), find the value of \(\displaystyle f'(x)\) at the point \(\displaystyle (-2,7)\)

Possible Answers:

\(\displaystyle 50\)

\(\displaystyle 7\)

\(\displaystyle -35\)

\(\displaystyle 49\)

\(\displaystyle -49\)

Correct answer:

\(\displaystyle -49\)

Explanation:

Given the function \(\displaystyle f(x)=10x^{2}-9x+1\), we can use the Power Rule

\(\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}\) for all \(\displaystyle n\neq0\) to find its derivative:

\(\displaystyle f'(x)=(2)10x^{2-1}-(1)9x^{1-1}+(0)=20x-9\).

Plugging in the \(\displaystyle x\)-value of the point \(\displaystyle (-2,7)\) into \(\displaystyle f'(x)\), we get 

\(\displaystyle f'(-2)=20(-2)-9=-40-9=-49\).

Example Question #53 : Derivatives

Find the derivative of \(\displaystyle y=(2x+4)(3x+2)\) at point \(\displaystyle (1,30)\).

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 12\)

\(\displaystyle 30\)

\(\displaystyle 8\)

\(\displaystyle 28\)

Correct answer:

\(\displaystyle 28\)

Explanation:

Use either the FOIL method to simplify before taking the derivative or use the product rule to find the derivative of the function.

The product rule will be used for simplicity.

\(\displaystyle y'=(2x+4)(3)+(3x+2)(2) = 6x+12 + 6x+4= 12x+16\)

Substitute \(\displaystyle x=1\).

\(\displaystyle y'(1)= 12(1)+16=28\)

 

Example Question #14 : Derivative At A Point

Given the function \(\displaystyle \small f(x)=2(x^2-1)^6\), calculate \(\displaystyle \small f'(2)\).

Possible Answers:

\(\displaystyle \small \small \small \small f'(2)=11,664\)

\(\displaystyle \small \small \small \small \small f'(2)=11,663\)

\(\displaystyle \small \small \small \small \small f'(2)=1458\)

\(\displaystyle \small \small \small \small \small f'(2)=2,916\)

Correct answer:

\(\displaystyle \small \small \small \small f'(2)=11,664\)

Explanation:

The derivative of \(\displaystyle \small f(x)=2(x^2-1)^6\) can be computed using the chain rule:

\(\displaystyle \small \small f'(x)=2\cdot 6\cdot 2x(x^2-1)^5=24x(x^2-1)^5\)

so now we just plug in \(\displaystyle \small x=2\):

\(\displaystyle \small \small \small f'(2)=24\cdot2(2^2-1)^5=48\cdot 3^5=11,664\)

Example Question #15 : Derivative At A Point

Given \(\displaystyle f(x)=x^{2}-7x+6\), what is the value of the slope at the point \(\displaystyle (2,3)\)?

Possible Answers:

\(\displaystyle -4\)

\(\displaystyle -3\)

\(\displaystyle 5\)

\(\displaystyle 3\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle -3\)

Explanation:

Slope is defined as the derivative of a function at a given point. By the Power Rule, 

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

\(\displaystyle f'(x)=(2)x^{2-1}-(1)7x^{1-1}+(0)6=2x-7\).

At \(\displaystyle (2,3)\) the \(\displaystyle x\)-value is \(\displaystyle x=2\), so the slope 

\(\displaystyle f'(2)=2(2)-7=4-7=-3\).

Example Question #16 : Derivative At A Point

Given \(\displaystyle f(x)=5x^{2}-7x+2\), what is the value of the slope at the point \(\displaystyle (-3,-1)\)?

Possible Answers:

\(\displaystyle -37\)

\(\displaystyle -36\)

\(\displaystyle -38\)

\(\displaystyle 37\)

\(\displaystyle 38\)

Correct answer:

\(\displaystyle -37\)

Explanation:

Slope is defined as the derivative of a function at a given point.

By the Power Rule, 

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

\(\displaystyle f'(x)=(2)5x^{2-1}-(1)7x^{1-1}+(0)2=10x-7\).

At \(\displaystyle (-3,-1)\) the \(\displaystyle x\)-value is \(\displaystyle x=-3\), so the slope 

\(\displaystyle f'(-3)=10(-3)-7=(-30)-7=-37\).

Example Question #17 : Derivative At A Point

Given \(\displaystyle f(x)=2x^{2}-9x+5\), what is the value of the slope at the point \(\displaystyle (4,-1)\)?

Possible Answers:

\(\displaystyle -7\)

\(\displaystyle 2\)

\(\displaystyle 5\)

\(\displaystyle -5\)

\(\displaystyle 7\)

Correct answer:

\(\displaystyle 7\)

Explanation:

Slope is defined as the derivative of a function at a given point.

By the Power Rule, 

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

\(\displaystyle f'(x)=(2)2x^{2-1}-(1)9x^{1-1}+0(5)=4x-9\).

At \(\displaystyle (4,-1)\) the \(\displaystyle x\)-value is \(\displaystyle x=4\), so the slope 

\(\displaystyle f'(4)=4(4)-9=16-9=7\).

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