答案:X 因为假设X=1，Y=2，Z=3 就可知道X，Y，Z的数值关系。
答：x²-y²-z²+2yz=x²-(y²-2yz+z²)=x²-(y-z)²=(x+y-z)(x-y+z)
x²-y²-z²+2yz=x²-(y²-2yz+z²)=x²-(y-z)²=[x+(y-z)][x-(y-z)]=(x+y-z)(x-y+z)
x²-y²-z²+2yz=x²-（y²+z²-2yz）=x^2-(y-z)^2=(x+y-z)(x-y+z)
