Question

(x+2y +3)的平方-[(x-2y)的平方-9]

Answer 1

（x+2y +3）^2-[（x-2y）^2-9]

=(x+2y+3)^2-(x-2y)^2+9

=(x+2y+3+x-2y)(x+2y+3-x+2y)+9

=(2x+3)(4y+3)+9

=8xy+6x+12y+9+9

=8xy+6x+12y+18

(x+y)^2(y-x)^2

=[(x+y)(y-x)]^2

=[x^2-y^2]^2

=x^4-2x^2y^2+y^4