Упростить (X-3y)(x+3y)-(x-3y)^2

Question

Упростить
(X-3y)(x+3y)-(x-3y)^2

Answer 1

(X-3y)(x+3y)-(x-3y)^2=(x^2-9y^2)-(x^2-6xy+9y^2)=x^2-9y^2-x^2+6xy-9y^2=6xy-18y^2=6y(x-3y)