先化简,再求值:[(1/2x+y)^2+(1/2x-y)^2](1/2x^2-2y^2),其中x=-2,y=-1
问题描述：
先化简,再求值:[(1/2x+y)^2+(1/2x-y)^2](1/2x^2-2y^2),其中x=-2,y=-1
答
原式=(1/4x²+xy+y²+1/4x²-xy+y²)(1/2x²-2y²)
=(1/2x²+2y²)(1/2x²-2y²)
=1/4x^4-y^4
=4-1
=3