# 4.4 Understand slope of a line  (Page 6/14)

 Page 6 / 14

Graph the line passing through the point $\left(-1,-3\right)$ whose slope is $m=4.$

## Solution

Plot the given point.

$\begin{array}{ccccc}\text{Identify the rise and the run.}\hfill & & \hfill m& =\hfill & 4\hfill \\ \text{Write 4 as a fraction.}\hfill & & \hfill \frac{\text{rise}}{\text{run}}& =\hfill & \frac{4}{1}\hfill \\ & & \hfill \text{rise}& =\hfill & 4\phantom{\rule{0.5em}{0ex}}\text{run}=1\hfill \end{array}$

Count the rise and run and mark the second point.

Connect the two points with a line.

You can check your work by finding a third point. Since the slope is $m=4$ , it can be written as $m=\frac{-4}{-1}$ . Go back to $\left(-1,-3\right)$ and count out the rise, $-4$ , and the run, $-1$ .

Graph the line with the point $\left(-2,1\right)$ and slope $m=3$ .

Graph the line with the point $\left(4,-2\right)$ and slope $m=-2$ .

## Solve slope applications

At the beginning of this section, we said there are many applications of slope in the real world. Let’s look at a few now.

The ‘pitch’ of a building’s roof is the slope of the roof. Knowing the pitch is important in climates where there is heavy snowfall. If the roof is too flat, the weight of the snow may cause it to collapse. What is the slope of the roof shown?

## Solution

$\begin{array}{cccc}\text{Use the slope formula.}\hfill & & & \phantom{\rule{4em}{0ex}}m=\frac{\text{rise}}{\text{run}}\hfill \\ \text{Substitute the values for rise and run.}\hfill & & & \phantom{\rule{4em}{0ex}}m=\frac{9}{18}\hfill \\ \text{Simplify.}\hfill & & & \phantom{\rule{4em}{0ex}}m=\frac{1}{2}\hfill \\ \text{The slope of the roof is}\phantom{\rule{0.2em}{0ex}}\frac{1}{2}.\hfill & & \\ & & & \begin{array}{c}\text{The roof rises 1 foot for every 2 feet of}\hfill \\ \text{horizontal run.}\hfill \end{array}\hfill \end{array}$

Use [link] , substituting the rise = 14 and run = 24.

$\frac{7}{12}$

Use [link] , substituting rise = 15 and run = 36.

$\frac{5}{12}$

Have you ever thought about the sewage pipes going from your house to the street? They must slope down $\frac{1}{4}$ inch per foot in order to drain properly. What is the required slope?

## Solution

$\begin{array}{cccc}\text{Use the slope formula.}\hfill & & & \phantom{\rule{5em}{0ex}}m=\frac{\text{rise}}{\text{run}}\hfill \\ & & & \phantom{\rule{5em}{0ex}}m=\frac{-\frac{1}{4}\text{inch}}{\text{1 foot}}\hfill \\ & & & \phantom{\rule{5em}{0ex}}m=\frac{-\frac{1}{4}\text{inch}}{\text{12 inches}}\hfill \\ \text{Simplify.}\hfill & & & \phantom{\rule{5em}{0ex}}m=-\frac{1}{48}\hfill \\ & & & \phantom{\rule{2em}{0ex}}\text{The slope of the pipe is}\phantom{\rule{0.2em}{0ex}}-\frac{1}{48}.\hfill \end{array}$

The pipe drops 1 inch for every 48 inches of horizontal run.

Find the slope of a pipe that slopes down $\frac{1}{3}$ inch per foot.

$-\frac{1}{36}$

Find the slope of a pipe that slopes down $\frac{3}{4}$ inch per yard.

$-\frac{1}{48}$

Access these online resources for additional instruction and practice with understanding slope of a line.

## Key concepts

• Find the Slope of a Line from its Graph using $m=\frac{\text{rise}}{\text{run}}$
1. Locate two points on the line whose coordinates are integers.
2. Starting with the point on the left, sketch a right triangle, going from the first point to the second point.
3. Count the rise and the run on the legs of the triangle.
4. Take the ratio of rise to run to find the slope.

• Graph a Line Given a Point and the Slope
1. Plot the given point.
2. Use the slope formula $m=\frac{\text{rise}}{\text{run}}$ to identify the rise and the run.
3. Starting at the given point, count out the rise and run to mark the second point.
4. Connect the points with a line.

• Slope of a Horizontal Line
• The slope of a horizontal line, $y=b$ , is 0.
• Slope of a vertical line
• The slope of a vertical line, $x=a$ , is undefined

## Practice makes perfect

Use Geoboards to Model Slope

In the following exercises, find the slope modeled on each geoboard.

$\frac{1}{4}$

$\frac{2}{3}$

$\frac{-3}{2}=-\frac{3}{2}$

$-\frac{2}{3}$

In the following exercises, model each slope. Draw a picture to show your results.

$\frac{2}{3}$

$\frac{3}{4}$

$\frac{1}{4}$

$\frac{4}{3}$

$-\frac{1}{2}$

$-\frac{3}{4}$

$-\frac{2}{3}$

$-\frac{3}{2}$

Use $m=\frac{\text{rise}}{\text{run}}$ to find the Slope of a Line from its Graph

In the following exercises, find the slope of each line shown.

$\frac{2}{5}$

$\frac{5}{4}$

$-\frac{1}{3}$

$-\frac{3}{4}$

$\frac{3}{4}$

$-\frac{5}{2}$

$-\frac{2}{3}$

$\frac{1}{4}$

Find the Slope of Horizontal and Vertical Lines

4x+7y=29,x+3y=11 substitute method of linear equation
substitute method of linear equation
Srinu
Solve one equation for one variable. Using the 2nd equation, x=11-3y. Substitute that for x in first equation. this will find y. then use the value for y to find the value for x.
bruce
I want to learn
Elizebeth
help
Elizebeth
I want to learn. Please teach me?
Wayne
1) Use any equation, and solve for any of the variables. Since the coefficient of x (the number in front of the x) in the second equation is 1 (it actually isn't shown, but 1 * x = x), use that equation. Subtract 3y from both sides (this isolates the x on the left side of the equal sign).
bruce
2) This results in x=11-3y. x is note in terms of y. Use that as the value of x and substitute for all x in the first equation. The first equation becomes 4(11-3y)+7y =29. Note that the only variable left in the first equation is the y. If you have multiple variable, then something is wrong.
bruce
3) Distribute (multiply) the 4 across 11-3y to get 44-12y. Add this to the 7y. So, the equation is now 44-5y=29.
bruce
4) Solve 44-5y=29 for y. Isolate the y by subtracting 44 from birth sides, resulting in -5y=-15. Now, divide birth sides by -5 (since you have -5y). This results in y=3. You now have the value of one variable.
bruce
5) The last step is to take the value of y from Step 4) and substitute into the 2nd equation. Therefore: x+3y=11 becomes x+3(3)=11. Then multiplying, x+9=11. Finally, solve for x by subtracting 9 from both sides. Therefore, x=2.
bruce
6) The ordered pair of (2, 3) is the proposed solution. To check, substitute those values into either equation. If the result is true, then the solution is correct. 4(2)+7(3)=8+21=29. TRUE! Finished.
bruce
At 1:30 Marlon left his house to go to the beach, a distance of 5.625 miles. He rose his skateboard until 2:15, and then walked the rest of the way. He arrived at the beach at 3:00. Marlon's speed on his skateboard is 1.5 times his walking speed. Find his speed when skateboarding and when walking.
divide 3x⁴-4x³-3x-1 by x-3
how to multiply the monomial
Two sisters like to compete on their bike rides. Tamara can go 4 mph faster than her sister, Samantha. If it takes Samantha 1 hours longer than Tamara to go 80 miles, how fast can Samantha ride her bike? Got questions? Get instant answers now!
how do u solve that question
Seera
Two sisters like to compete on their bike rides. Tamara can go 4 mph faster than her sister, Samantha. If it takes Samantha 1 hours longer than Tamara to go 80 miles, how fast can Samantha ride her bike?
Seera
Speed=distance ÷ time
Tremayne
x-3y =1; 3x-2y+4=0 graph
Brandon has a cup of quarters and dimes with a total of 5.55\$. The number of quarters is five less than three times the number of dimes
app is wrong how can 350 be divisible by 3.
June needs 48 gallons of punch for a party and has two different coolers to carry it in. The bigger cooler is five times as large as the smaller cooler. How many gallons can each cooler hold?
Susanna if the first cooler holds five times the gallons then the other cooler. The big cooler holda 40 gallons and the 2nd will hold 8 gallons is that correct?
Georgie
@Susanna that person is correct if you divide 40 by 8 you can see it's 5 it's simple
Ashley
@Geogie my bad that was meant for u
Ashley
Hi everyone, I'm glad to be connected with you all. from France.
I'm getting "math processing error" on math problems. Anyone know why?
Can you all help me I don't get any of this
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Did anyone else have trouble getting in quiz link for linear inequalities?
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