The slope-intercept equation is y=mx+b.
The slope formula is
Our three points are (5,5), (-5,-7) and (0,-1)
Using our slope formula our slope becomes
Then, if we use one of our points (pick whichever you want, although (0,1) is the easiest) to solve the equation. So, . When we solve for x and y, we get -1=0+b, or b=-1.
When we plug that back into the equation, we get.