20(x+y)+x+y=20(x+y)+(x+y)=21(x+y)X平方-y平方+ax+ay=(x+y)(x-y)+a(x+y)=(x+y)(x-y+a)a平方-2ab+b平方-c平方=(a-b)²-c²=(a-b+c)(a-b-c)x立方+x平方y-xy2-y立方=x²(x+y)-y²(x+y)=(x+y)(x²-...