x+y分之x平方-y平方-2x-2y其中x=3y=3分之1
问题描述：
x+y分之x平方-y平方-2x-2y其中x=3y=3分之1
答
(x^2-y^2)/(x+y)-2x-2y
=(x-y)(x+y)/(x+y)-2x-2y
=x-y-2x-2y
=-x-3y
=-3-3*1/3
=-3-1
=-4还有一道题a平方-a=0求a+2分之a-1乘啊平方-2a+1分之a平方-4除以a平方-1分之一多给你5分(a-1)/(a+2)*(a^2-4)/(a^2-2a+1)÷1/(a^2-1) =(a-1)/(a+2)*(a^2-4)/(a^2-2a+1)*(a^2-1) =(a-1)/(a+2)*(a-2)(a+2)/(a-1)^2*(a-1)(a+1) =(a-1)/(a+2)*(a-2)(a+2)/(a-1)*(a+1) =(a-1)*(a-2)/(a-1)*(a+1) =(a-2)*(a+1) =a^2-a-2 =0-2 =-2