(y-y0)/(y0-y1)=(x-x0)/(x0-x1)
y-y0=(x-x0)(y0-y1)/(x0-x1)
y=(x-x0)(y0-y1)/(x0-x1) +y0
y=[(y0-y1)/(x0-x1)]x+[y0-x0(y0-y1)/(x0-x1)]