Answer:
y-y1 = m (x-x1)
where
m is the slope
and (x1,y1) is one of the points given.
You have been given 2 points (-12,8) and (9,1). You can call one of them (x1,y1) and the other (x2,y2). It doesn't matter which one is which.
But before we go further, we need to determine the slope.
We can do this from the points as well.
y2-y1
m = ---------
x2-x1
Let's say
(x1,y1) = (-12,8)
(x2,y2) = (9,1)
This gives us a slope of
y2-y1 1-8 -7 -1
m = --------- = ---------- = ---- = ---
x2-x1 9-(-12) 21 3
Now that we have everything we need
y-8 = (-1/3)[x-(-12)]
Distribute the -1/3
y-8 = (-1/3)x -4
If we add 8 to both sides we have the equation in the slope intercept form (y=mx+b)
y = (-1/3)x + 4
