x^2-y^2-z^2-2yz
问题描述：
x^2-y^2-z^2-2yz
答
原式=x²-(y²+2yz+z²)
=x²-(y+z)²
=(x+y+z)(x-y-z)=x²-(y+z)²=(x+y+z)(x-y-z) 后面怎么成了x-y-z平方差x-(y+z)