Calculus 1 : How to find slope by graphing functions

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #1 : Slope

What is the slope of the tangent line of f(x) = 3x4 – 5x3 – 4x at x = 40?

Possible Answers:

684,910

None of the other answers

331,841

743,996

768,000

Correct answer:

743,996

Explanation:

The first derivative is easy:

f'(x) = 12x3 – 15x2 – 4

The slope of the tangent line is found by calculating f'(40) = 12 * 403 – 15 * 402 – 4 = 768,000 – 24,000 – 4 = 743,996

Example Question #1 : How To Find Slope By Graphing Functions

Find the slope of the line tangent to \(\displaystyle y(b)\) when \(\displaystyle b\) is equal to \(\displaystyle 6\).

\(\displaystyle y(b)=b^7-b^5+4b^2\)

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle 320160\)

\(\displaystyle -320160\)

\(\displaystyle 3216\)

\(\displaystyle 3160\)

Correct answer:

\(\displaystyle 320160\)

Explanation:

To find the slope of a tangent line, we need to find the first derivative of the function at that point. In other words, we need y'(6).

\(\displaystyle y(b)=b^7-b^5+4b^2\)

Taking the first derivative using the Power Rule \(\displaystyle f(x)=x^n \rightarrow f'(x)=nx^{n-1}\) we get the following.

\(\displaystyle y'(b)=7b^6-5b^4+8b\)

Substituting in 6 for b and solving we get:

\(\displaystyle y'(6)=7\cdot6^6-5\cdot6^4+8\cdot6=320160\).

So our answer is 320160

Example Question #2 : How To Find Slope By Graphing Functions

Find function which gives the slope of the line tangent to \(\displaystyle j(x)\).

\(\displaystyle j(x)=\frac{4x^5}{5}-x^4+x^2\)

Possible Answers:

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

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

\(\displaystyle 3x^4-12x^3+2x\)

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

\(\displaystyle 16x^3-12x^2+2\)

Correct answer:

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

Explanation:

To find the slope of a tangent line, we need the first derivative.

Recall that to find the first derivative of a polynomial, we need to decrease each exponent by one and multiply by the original number.

\(\displaystyle j(x)=\frac{4x^5}{5}-x^4+x^2\)

\(\displaystyle j'(x)=4x^4-4x^3+2x\)

Example Question #2 : Slope

Find the slope of the line tangent to \(\displaystyle b(s)\) at \(\displaystyle s=16\).

\(\displaystyle b(s)=14s^2+6s-4\)

Possible Answers:

\(\displaystyle 343\)

\(\displaystyle 544\)

\(\displaystyle 545\)

\(\displaystyle 454\)

\(\displaystyle 144\)

Correct answer:

\(\displaystyle 454\)

Explanation:

The slope of the tangent line can be found easily via derivatives. To find the slope of the tangent line at s=16, find b'(16) using the power rule on each term which states:

\(\displaystyle f(x)=x^n \rightarrow f'(x)=nx^{n-1}\)

Applying this rule we get:

\(\displaystyle b(s)=14s^2+6s-4\)

\(\displaystyle b'(s)=28s+6\)

\(\displaystyle b'(16)=28\cdot 16+6=454\)

Therefore, the slope we are looking for is 454.

 

Example Question #3 : Slope

Find the slope of \(\displaystyle f(x)\) at \(\displaystyle x=\pi\).

\(\displaystyle f(x)=ln(x^2 +2)-cos(17x)\)

Possible Answers:

\(\displaystyle 17.529\)

\(\displaystyle 0.629\)

\(\displaystyle 0.529\)

\(\displaystyle 0\)

\(\displaystyle 10.229\)

Correct answer:

\(\displaystyle 0.529\)

Explanation:

To find the slope of the line at that point, find the derivative of f(x) and plug in that point. 

\(\displaystyle f'(x)= \frac{2x}{x^2 +2}+17sin(17x)\)

Remember that the derivative of \(\displaystyle cos(bx) = -bsin(bx)\) and the derivative of   \(\displaystyle ln(u) = \frac{u'}{u}\)

Now plug in \(\displaystyle x=\) \(\displaystyle \pi\)

\(\displaystyle f'(\pi )=\frac{2\pi}{\pi ^2 +2}=.529\)

Example Question #1 : How To Find Slope By Graphing Functions

Find the slope of\(\displaystyle f(x)\) at \(\displaystyle x=2\) given \(\displaystyle f''(x)\). Assume the integration constant is zero.

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

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 2\)

\(\displaystyle 10\)

\(\displaystyle 4\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 6\)

Explanation:

The first step here is to integrate \(\displaystyle f''(x)\) in order to get \(\displaystyle f'(x)\).

\(\displaystyle \int f''(x)dx =\int(x+2)dx=\frac{x^2}{2} +2x +C\)

Here the problem tells us that the integration constant \(\displaystyle C=0\), so

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

Plug in \(\displaystyle x=2\) here

\(\displaystyle f'(2)=6\)

Example Question #1 : Slope

Consider the curve

\(\displaystyle y=ln[x]+3x^2\).

What is the slope of this curve at \(\displaystyle x=1.5\)?

Possible Answers:

\(\displaystyle \frac{34}{3}\)

\(\displaystyle 9\)

\(\displaystyle \frac{29}{3}\)

\(\displaystyle \frac{17}{3}\)

\(\displaystyle 12\)

Correct answer:

\(\displaystyle \frac{29}{3}\)

Explanation:

The slope of a curve at any point is equal to the derivative of the curve at that point.

Remembering that the derivative of \(\displaystyle ln(x)\rightarrow \frac{1}{x}\) and using the power rule on the second term we find the derivative to be:

\(\displaystyle \frac{dy}{dx}=\frac{1}{x}+6x\).

Pluggin in \(\displaystyle x=1.5\) we find that the slope is \(\displaystyle \frac{29}{3}\).

Example Question #2 : Slope

Find the line tangent to \(\displaystyle y=e^{5x}\) at \(\displaystyle x=3\).

Possible Answers:

\(\displaystyle y=5e^{15}x-3\)

\(\displaystyle y=e^{15}x+e^{15}\)

\(\displaystyle y=5e^{15}x-14e^{15}\)

\(\displaystyle y=5e^{15}x-2e^{15}\)

\(\displaystyle y=5e^{15}x-14e^{15}\)

Correct answer:

\(\displaystyle y=5e^{15}x-14e^{15}\)

Explanation:

Find the line tangent to \(\displaystyle y=e^{5x}\) at \(\displaystyle x=3\).

 

First, we find \(\displaystyle y\):

\(\displaystyle y=e^{5x}=e^{5\cdot3}=e^{15}\)

Next, we find the derivative:

\(\displaystyle \frac{dy}{dx}=5e^{5x}\)

Therefore, the slope at \(\displaystyle x=3\) is:

\(\displaystyle \frac{dy}{dx}=5e^{5x}=5e^{5\cdot3}=5e^{15}\).

Using point-slope form, we can write the tangent line:

\(\displaystyle y=5e^{15}(x-3)+e^{15}\)

Simplifying this gives us:

\(\displaystyle y=5e^{15}x-14e^{15}\)

Example Question #9 : Slope

An isosceles triangle has one point at \(\displaystyle (6,2)\), one point at \(\displaystyle (6,10)\) and one point on the \(\displaystyle y\)-axis. What is the slope of the line between the point on the \(\displaystyle y\)-axis and \(\displaystyle (6,10)\)?

Possible Answers:

\(\displaystyle 2\)

\(\displaystyle 5/3\)

\(\displaystyle 2/3\)

\(\displaystyle 1/2\)

\(\displaystyle 3/2\)

Correct answer:

\(\displaystyle 2/3\)

Explanation:

The other point of the triangle must be at \(\displaystyle (0,6)\) as it must be equidistant from the other two points of the triangle. Since all points on the y-axis are \(\displaystyle 6\) units away from the other points in the \(\displaystyle x\) direction, the third point must be equidistant in the \(\displaystyle y\) direction from both \(\displaystyle (6,2)\) and \(\displaystyle (6,10)\). The distance between these points is \(\displaystyle 8\), so the third point must have a y-value of \(\displaystyle 2+(8/2)=6\). The third point is now at \(\displaystyle (0,6)\) so the slope of the line from \(\displaystyle (0,6)\) to \(\displaystyle (6,10)\) is as follows.

\(\displaystyle \\m=\frac{y_2-y_1}{x_2-x_1}\\ \\=\frac{10-6}{6-0}\\ \\ =\frac{4}{6}=\frac{2}{3}\)

Example Question #2 : How To Find Slope By Graphing Functions

What is the slope of the line tangent to the graph of \(\displaystyle f(x)=\sin(2x)\) at \(\displaystyle x=\pi/2\)?

Possible Answers:

\(\displaystyle -2\)

\(\displaystyle -1/2\)

\(\displaystyle 0\)

\(\displaystyle 2\)

\(\displaystyle 1/2\)

Correct answer:

\(\displaystyle -2\)

Explanation:

We must take the derivative of the function using the chain rule yielding \(\displaystyle f'(x)=2\cos(2x)\).

The chain rule is \(\displaystyle [f(g(x))]'=f'(g(x))\cdot g'(x)\).

Also remember that the derivative of \(\displaystyle sin(x)\) is \(\displaystyle cos(x)\).

Applying these rules we get the following.

\(\displaystyle \\f(x)=\sin(2x)\\ \\ u=2x\\ \\ \frac{du}{dx}=2\\ \\ \frac{d}{dx}\sin(u)=\cos(u)\frac{du}{dx}=2\cos(u)\\ \\ f'(x)=2\cos(2x)\)

Plugging in the value for \(\displaystyle x\) we get \(\displaystyle 2\cos(\pi)\) which is \(\displaystyle -2\).

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