Question

(8h-9)(9+8h)-(h+9)(h-9)

Answer 1

(8h-9)(9+8h)-(h+9)(h-9)=72h+64h²-81-72h-(h²-81)=64h²-81-h²+81=63h²

Answer 2

$(8h-9)(9+8h)-(h+9)(h-9)=(8h-9)(8h+9)-(h^2-9^2)=$

$=(8h)^2-9^2-h^2+9^2=8^2h^2-h^2-9^2+9^2=64h^2-h^2=63h^2$