(x-y)分之x-(x+y)分之y+(x的2次方-y的2次方)分之2xy=(x-y)分之x-(x+y)分之y+(x-y)(x+y)分之2xy=(x-y)(x+y)分之[x(x+y)-y(x-y)+2xy]=(x-y)(x+y)分之(x平方＋2xy＋y平方)=(x-y)(x+y)分之(x+y)平方=(x-y)分之(x+y)...