化简：(x+y)(x-y)-2(4-y^2+1/2x^2) 赶紧回答吧,（x+y)(x-y)-2[4-y^2+(1/2)x^2] 是化简，不是计算！

化简：(x+y)(x-y)-2(4-y^2+1/2x^2) 赶紧回答吧,（x+y)(x-y)-2[4-y^2+(1/2)x^2] 是化简，不是计算！
化简：(x+y)(x-y)-2(4-y^2+1/2x^2) 赶紧回答吧,
（x+y)(x-y)-2[4-y^2+(1/2)x^2] 是化简，不是计算！

化简：(x+y)(x-y)-2(4-y^2+1/2x^2) 赶紧回答吧,（x+y)(x-y)-2[4-y^2+(1/2)x^2] 是化简，不是计算！
x+y)(x-y)-2(4-y^2+1/2x^2) =x^2-y^2-8+2y^2-x^2=y^2-8