【(2/1x-y)平方+(2/1x+y)平方】（2/1x的平方--2y平方)
=(1/4x²-xy+y²+1/4x²+xy+y²(1/2x²-2y²)
=(1/2x²+2y²)(1/2x²-2y²)
=1/4x^4-4y^4
x^4是想的4次方
y^4是y的4次方