Answer:
Red Line: y =
- 9
Blue Line: y = -2x + 6
Yellow Line: y =
+ 9
Explanation:
y=mx+b is the slope-intercept formula for a line. This means that this equation tells you the y-intercept of a line as well as the slope of a line. In this formula, m is equal to the slope, and b is equal to the y-intercept.
The Y-intercept of a line is where the line crosses the y-axis.
The slope of a line is how much the line is increasing or decreasing by. You can calculate this number by dividing how much the line increases by the y-axis by how much the line increases on the x-axis. Essentially, you divide the line's rise over its run, or the change in y over the change in x.
Slope formula:

and
make up one coordinate, and
and
make up another. Both of these points must land on the same line--the line you are trying to find the slope of.
Red Line:
In this photo, we can clearly see what the y-intercept is. The slope intercept is -9, so b = -9.
To find the slope, you take two points and find the difference of their y-values and divide that by the difference of their x-values.
On the red line, we can see that the line crosses points (2, -4) and (0, -9). Let's find the slope by subtracting the y-values first:
-4 - (-9) = 5
5 is your change in y values, or your rise!
Now, let's subtract the x-values:
2 - 0 = 2
2 is your change in x values, or your run!
In order to finally find the slope of this line, you divide your change in y by your change in x. Therefore, you divide 5 by 2.
Your slope is
. It's okay to leave slopes in fraction form!
So, now you plug in your slope and y-intercept that we found before into your formula! Remember:
b = y-intercept
m = slope
So, y =
- 9 is the formula for your line!
Red line: y =
- 9
Now, we repeat the process with the other lines. Let's do the blue line:
We can see that the y-intercept is 6. So, b = 6.
Now, let's calculate the slope. Let's find points on the blue line that we can use!
Point 1: (0, 6)
Point 2: (1, 4)
Let's subtract the y values:
6 - 4 = 2
Let's subtract the x values:
0 - 1 = -1
When we divide 2 (our change in y) by -1 (our change in x), we are left with -2 as our slope!
Slope = -2
So, when we plug everything into our equation, we get:
y = -2x + 6
Blue Line: y = -2x + 6
Now, for the last one!
We can see that the y-intercept is 9, so b = 9.
Let's calculate the slope:
Point 1: (0, 9)
Point 2: (3, 8)
Subtract the y-values:
9 - 8 = 1
Subtract the x-values:
0 - 3 = -3
Divide the change in y by the change in x:
1 ÷ -3 =

Slope =

Plug everything in!
y =
+ 9
Yellow Line: y =
+ 9