3(x-y)²(x+y)²-9(x+y)³(y-x)³

问题描述:

3(x-y)²(x+y)²-9(x+y)³(y-x)³

3(x-y)²(x+y)²-9(x+y)³(y-x)³=3(x-y)²(x+y)²+9(x+y)³(x-y)³=3(x-y)²(xy)²[1+3(x+y)(x-y)]=3(x-y)²(x+y)²(1+3x²-3y²)...