初二数学题，在线等，会追加分

(3xy-2x^2+1/2y^2)(3xy+2x^2-1/2y^2)

=(3xy)^2-(2x^2-1/2y^2)^2

=9x^2y^2-4x^4-1/4y^4+2x^2y^2

=11x^2y^2-4x^4-1/4y^4

(3xy-2x^2+1/2y^2)(3xy+2x^2-1/2y^2)
=[3xy-(2x^2-1/2y^2)][3xy+(2x^2-1/2y^2)]
=9x2y2-(2x^2-1/2y^2)2
那个2x^2中间的是什么数学符号不知道,没法向下继续了

(a+b)(a-b)=a^2-b^2
a=3xy
b=2x^2-1/2y^2

剩下的用公式自己算

就是这(3xy-2x^2+1/2y^2)(3xy+2x^2-1/2y^2)

=(3xy)^2-(2x^2-1/2y^2)^2

=9x^2y^2-4x^4-1/4y^4+2x^2y^2

=11x^2y^2-4x^4-1/4y^4