y=mx+b
m=slope
b=yitercept
slope for 2 points (x1,y1) and (x2,y2)
slope=(y2-y1)/(x2-x1)
bettween (4,-1) and (-4,3)
slope=(3-(-1))/(-4-4)=(3+1)/-8=4/-8=-1/2
slope=-1/2
y=-1/2x+b
sub apoint and solve
(x,y)
(4,-1)
if x=4, y=-1
-1=-1/2(4)+b
-1=-2+b
add 2
1=b
y=-1/2x+1
