已知x=a+b,y=a-b,求(x²+y²)²-(x²-y²)²的值
问题描述：
已知x=a+b,y=a-b,求(x²+y²)²-(x²-y²)²的值
答
原式=[(x²+y²)+(x²-y²)][(x²+y²)-(x²-y²)]=)2x1N)(2y²)=4(xy)²=4[(a+b)(a-b)]²=4(a²-b²)²=4a^4-8a²b²+4b^4