Algebra 1 : How to find slope of a line

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #171 : Equations Of Lines

What is the slope of the line \(\displaystyle 3y-9x=15\)?

Possible Answers:

\(\displaystyle -3\)

\(\displaystyle 5\)

\(\displaystyle 3\)

\(\displaystyle 9\)

\(\displaystyle -9\)

Correct answer:

\(\displaystyle 3\)

Explanation:

To easily find the slope of the line, you can rearrange the equation to the \(\displaystyle y=mx+b\) form. To do this, isolate the \(\displaystyle y\) by moving the \(\displaystyle x\) to the other side of the equation. This gives you \(\displaystyle 3y=9x+15\). Then, divide both sides by 3 to isolate the \(\displaystyle y\), which leaves you with \(\displaystyle y=3x+5\). Now, the equation is in the \(\displaystyle y=mx+b\) form, and you can easily see that the slope is 3.

Example Question #171 : Equations Of Lines

What is the slope of the line depicted by the equation?

\(\displaystyle 6x+3y=15\)

Possible Answers:

\(\displaystyle m=\frac{5}{2}\)

\(\displaystyle m=\frac{2}{5}\)

\(\displaystyle m=-\frac{1}{2}\)

\(\displaystyle m=-2\)

Correct answer:

\(\displaystyle m=-2\)

Explanation:

The equation is written in standard from: \(\displaystyle \small Ax+By=C\). In this format, the slope is \(\displaystyle \small -\frac{A}{B}\).

\(\displaystyle 6x+3y=15\)

In our equation, \(\displaystyle \small A=6\) and \(\displaystyle \small B=3\).

\(\displaystyle \small m=-\frac{A}{B}=-\frac{6}{3}\)

\(\displaystyle \small -\frac{6}{3}=-2\)

Example Question #82 : Slope And Line Equations

Find the slope of the line defined by the equation \(\displaystyle 4x - 6y = 15\).

Possible Answers:

\(\displaystyle -\frac{2}{3}\)

\(\displaystyle -\frac{3}{2}\)

\(\displaystyle -24\)

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

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

Correct answer:

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

Explanation:

\(\displaystyle 4x - 6y = 15\)

\(\displaystyle -4x + 4x - 6y = -4x + 15\)

\(\displaystyle - 6y = -4x + 15\)

\(\displaystyle - 6y \div (-6)=\left ( -4x + 15 \right )\div (-6)\)

\(\displaystyle y =\frac{2}{3 }x- \frac{5}{2}\)

The slope is the coefficient of \(\displaystyle x\)\(\displaystyle m = \frac{2}{3}\)

Example Question #11 : How To Find Slope Of A Line

Find the slope of the line that includes points \(\displaystyle (5,-4)\) and \(\displaystyle (8,-2)\).

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle \frac{6}{13}\)

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

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

\(\displaystyle \frac{1}{6}\)

Correct answer:

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

Explanation:

Use the slope formula: 

\(\displaystyle m = \frac{y_{2}-y_{1}}{x_{2}-x_{1}} = \frac{-2-(-4)}{8-5} = \frac{2}{3}\)

Example Question #421 : Functions And Lines

Find the slope of the line that includes points \(\displaystyle (5,4)\) and \(\displaystyle (8,-2)\).

Possible Answers:

\(\displaystyle \frac{1}{10}\)

\(\displaystyle \frac{6}{13}\)

\(\displaystyle -\frac{1}{2}\)

\(\displaystyle \frac{13}{6}\)

\(\displaystyle -2\)

Correct answer:

\(\displaystyle -2\)

Explanation:

Use the slope formula: 

\(\displaystyle m = \frac{y_{2}-y_{1}}{x_{2}-x_{1}} = \frac{-2-4}{8-5} = \frac{-6}{3} = -2\)

 

Example Question #84 : Slope And Line Equations

Line \(\displaystyle A\) is a straight line that passes through these points on a graph:(-4,0) (0,3) and (4,6). What is the slope of line \(\displaystyle A\)?

Possible Answers:

There is no straight line that passes through these three points. 

\(\displaystyle -\frac{3}{4}\)

\(\displaystyle -\frac{4}{3}\)

\(\displaystyle \frac{4}{3}\)

\(\displaystyle \frac{3}{4}\)

Correct answer:

\(\displaystyle \frac{3}{4}\)

Explanation:

To calculate the slope of a line, we pick two points, and calculate the change in \(\displaystyle y\) divided by the change in \(\displaystyle x\). To calculate the change in value, we use subtraction. So, 

slope = \(\displaystyle \frac{\text{Change in Y}}{\text{Change in X}} = \frac{y_2-y_1}{x_2-x_1}\) 

So we can pick any two points and plug them into this formula. Let's choose (0,3) and (4,6). We get 

\(\displaystyle \frac{6-3}{4-0}= \frac{3}{4}\)

Example Question #172 : Equations Of Lines

The following equation describes a straight line.

\(\displaystyle y=-2x-3\)

Identify the slope and y-intercept of the line.

Possible Answers:

None of these

Slope: \(\displaystyle \small -2\)

Y-intercept: \(\displaystyle \small (-3,0)\)

Slope: \(\displaystyle \small -3\)

Y-intercept: \(\displaystyle \small (-2,0)\)

Slope: \(\displaystyle \small -3\)

Y-intercept: \(\displaystyle \small (0,-2)\)

Slope: \(\displaystyle \small -2\)

Y-intercept: \(\displaystyle \small (0,-3)\)

Correct answer:

Slope: \(\displaystyle \small -2\)

Y-intercept: \(\displaystyle \small (0,-3)\)

Explanation:

The general formula of a straight line is \(\displaystyle y=mx+b\), where \(\displaystyle \small m\) is the slope and \(\displaystyle \small b\) is the y-intercept.

To evaluate our original equation, we can compare it to this formula.

\(\displaystyle y=mx+b\)

\(\displaystyle y=-2x-3\)

The slope is \(\displaystyle \small -2\) and the y-intercept is at \(\displaystyle \small -3\). Since the y-intercept is a point on the line, it is written as \(\displaystyle \small (0,-3)\).

 

Example Question #18 : How To Find Slope Of A Line

Find the slope of the line defined by the equation \(\displaystyle 2x + 6y = 15\).

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle -3\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle - \frac{1}{3}\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle - \frac{1}{3}\)

Explanation:

Rewrite in slope-intercept form:

\(\displaystyle 2x + 6y = 15\)

\(\displaystyle -2x + 2x + 6y = -2x +15\)

\(\displaystyle 6y = -2x +15\)

\(\displaystyle 6y \div 6= \left (-2x +15 \right )\div 6\)

\(\displaystyle y= - \frac{1}{3}x +\frac{5}{2}\)

The slope is the coefficient of \(\displaystyle x\):

 \(\displaystyle m = - \frac{1}{3}\)

Example Question #14 : How To Find Slope Of A Line

Identify the slope and y-intercept of the following function.

\(\displaystyle y=-\frac{1}{3}x-2\)

Possible Answers:

Slope: \(\displaystyle 2\)

Y-intercept: \(\displaystyle (0,3)\)

Slope: \(\displaystyle 3\)

Y-intercept: \(\displaystyle (0,\frac{1}{2})\)

Slope: \(\displaystyle -3\)

Y-intercept:\(\displaystyle (0,-\frac{1}{2})\)

Slope:\(\displaystyle -\frac{1}{3}\)

Y-intercept: \(\displaystyle (0,-2)\)

Slope: \(\displaystyle \frac{1}{3}\)

Y-intercept: \(\displaystyle (0,-2)\)

Correct answer:

Slope:\(\displaystyle -\frac{1}{3}\)

Y-intercept: \(\displaystyle (0,-2)\)

Explanation:

This function describes a straight line. We can compare the given equation with the formula for a straight line in slope-intercept form.

\(\displaystyle y=-\frac{1}{3}x-2\)

\(\displaystyle y=mx+b\)

In the formula, \(\displaystyle m\) is the slope and \(\displaystyle b\) is the y-intercept. Looking at our given equation, we can see that \(\displaystyle m=-\frac{1}{3}\) and \(\displaystyle b=-2\).

Since the y-intercept is a point, we want to write it in point notation: \(\displaystyle (0,-2)\)

Example Question #11 : How To Find Slope Of A Line

Determine the slope and y-intercept of the following equation.

\(\displaystyle 1-10x+5y=2\)

Possible Answers:

Slope: \(\displaystyle 7\)

Y-intercept: \(\displaystyle (0,\frac{1}{9})\)

None of these

Slope: \(\displaystyle \frac{1}{2}\)

Y-intercept: \(\displaystyle (0,-3)\)

Slope: \(\displaystyle -3\)

Y-intercept: \(\displaystyle (0,\frac{1}{2})\)

Slope: \(\displaystyle 2\)

Y-intercept: \(\displaystyle (0,\frac{1}{5})\)

Correct answer:

Slope: \(\displaystyle 2\)

Y-intercept: \(\displaystyle (0,\frac{1}{5})\)

Explanation:

\(\displaystyle 1-10x+5y=2\)

You see that this equation is not written explicitly in terms of \(\displaystyle x\). Before we can determine the slope and y-intercept, we need to write the equation explicitly in terms of \(\displaystyle x\) by solving for \(\displaystyle y\).

First, add \(\displaystyle 10x\) to both sides.

\(\displaystyle 1-10x+10x+5y=10x+2\)

\(\displaystyle 1+5y=10x+2\)

Then subtract \(\displaystyle 1\) to both sides.

\(\displaystyle 1-1+5y=10x+2-1\)

\(\displaystyle 5y=10x+1\)

Finally, divide by \(\displaystyle 5\).

\(\displaystyle \frac{5y}{5}=\frac{10x+1}{5}\)

\(\displaystyle y=2x+\frac{1}{5}\)

Now that the equation is explicitly in terms of \(\displaystyle x\), we can compare it to the general formula of a straight line in slope-intercept form.

\(\displaystyle y=mx+b\)

In this equation, \(\displaystyle m\) is equal to the slope and \(\displaystyle b\) is equal to the y-intercept. Comparing our given equation to the formula, we can see that \(\displaystyle m=2\) and \(\displaystyle b=\frac{1}{5}\).

Since the y-intercept is a point, we will want to write it in point notation: \(\displaystyle (0,\frac{1}{5})\).

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