Answer:
7
Step-by-step explanation:
The formula for slope is [tex]\frac{y_2-y_1}{x_2-x_1}=m[/tex] where [tex]m[/tex] is the slope and [tex](x_1,y_1) \text{ and } (x_2,y_2)[/tex] are points on the line.
We can use that formula but I like to line my points up vertically and subtract and then put 2nd difference over 1st difference.
(-4,r)
minus
(4,-1)
--------
-8 r-(-1)
So we have:
[tex]\frac{r+1}{-8}=-1[/tex]
Multiply both sides by -8:
[tex]r+1=8[/tex]
Subtract 1 on both sides:
[tex]r=8-1=7[/tex].
Let's check:
(-4,7)
minus
(4,-1)
-------
-8 8
So the slope is 8/-8=-1 which is what we wanted.
So the value for r being 7 has been checked and verified.
