(a+1)x的平方+(a+1)x-a-1
=（a+1)x²+(a+1)x-(a+1)
=(a+1)(x²+x-1)
x（x-y-z）+y（y-x+z）+z（z-x+y）
=x(x-y-z)-y(x-y-z)-z(x-y-z)
=(x-y-z)²
3xy（x+y）-5y（x+y）-x-y
=3xy(x+y)-5y(x+y)-(x+y)
=(x+y)(3xy-5y-1)