把(X-Y)和(X+Y)各看作一个字母因式,合并同类项3（X+Y)²-（X-Y)+2(X+Y)²+（X-Y)-5(X+Y)²=

把(X-Y)和(X+Y)各看作一个字母因式,合并同类项3（X+Y)²-（X-Y)+2(X+Y)²+（X-Y)-5(X+Y)²=
把(X-Y)和(X+Y)各看作一个字母因式,合并同类项3（X+Y)²-（X-Y)+2(X+Y)²+（X-Y)-5(X+Y)²=

把(X-Y)和(X+Y)各看作一个字母因式,合并同类项3（X+Y)²-（X-Y)+2(X+Y)²+（X-Y)-5(X+Y)²=
3（X+Y)²-（X-Y)+2(X+Y)²+（X-Y)-5(X+Y)²
=3（X+Y)²+2(X+Y)²-5(X+Y)²-（X-Y)+（X-Y)
=0

全都抵消了，等于零