y=2x+b
4x^2+9(2x+b)^2-36=0
40x^2+36bx+9b^22-36=0
x1+x2=-35b/40=-7b/8
x/2=-7b/16
(y1+y2)/2=y=(x1+x2)+b
=-7b/8+b=b/8
x/y=(-7/16)*8=-7/2
-7y=2x
2x+7y=0