1 为了便于理解,将（x-y）设为b,也可不设则原式=b^2-4b+4-a^2=(b-2)^2-a^2=(b-a+2)(b+a+2)=(x-y-a-2)(x-y-2+a)2 =(x^3+y^3)(x^3-y^3)这里用了立方差,若无要求分到上一步即可 =(x+y)(x^2-xy+y^2)(x-y)(x^2+xy+y^2)...