(x-y)五次方(x+y)四次方÷(y-x)三次方÷(x+y)二次方+(x平方+y平方)二次方
=-（x-y)^2(x+y)^2+(x^2+y^2)^2
=(x^2+y^2)^2-(x^2-y^2)^2
=(x^2+y^2+x^2-y^2)(x^2+y^2-x^2+y^2)
=4x^2 y^2