Question

(y-9)(y^2+9y+81)

Answer 1

(y-9)(y^2+9y+81)



y(y^2+9y+81)-9(y^2+9y+81)



(y)*(y^2)+(y)*(9y)+(y)*(81)+(-9)*(y^2)+(-9)*(9y)+(-9)*(81)



y^3+9*y^2+81*y-9*y^2-81*y-729



y^3-729



So (y-9)(y^2+9y+81) = y^3-729


Note: this is a difference of cubes