Use (x-2)(x+7) = x²+5x-14
Prove  (y²+9y)(y²+9y+9)  = (y²+9y+2)² + 5(y² +9y)-4

let z = y²+9y+2,
(y²+9y+2)² + 5(y² +9y) - 4  =  z² + 5(z - 2) - 4 
                         = z² + 5z - 14
                         =(z-2)(z+7)
                         =(y²+9y)(y²+9y+9)