先化简,再求值:[(3x-3y)/(y平方-x平方)+(x平方-2xy+y平方)/(x平方-y平方)-(x平方-x+6)/(x+2)]/(x+y),其中x=3,y=1
问题描述：
先化简,再求值:[(3x-3y)/(y平方-x平方)+(x平方-2xy+y平方)/(x平方-y平方)-(x平方-x+6)/(x+2)]/(x+y),其中x=3,y=1
答
[(3x-3y)/(y平方-x平方)+(x平方-2xy+y平方)/(x平方-y平方)-(x平方-x+6)/(x+2)]/(x+y)
=:[3 (x-y) / (1-9) + (x-y）平方 / (9-1) - X(x-1）+6 / (3+2)] / (3+1)
=[ -6/8+4/8-12/5]/4
= -53/80
答
[(3x-3y)/(y平方-x平方)+(x平方-2xy+y平方)/(x平方-y平方)-(x平方-x+6)/(x+2)]/(x+y)=【-3/(x+y)+(x-y)/(x+y)-(x-3)]】/(x+y)=[(-3+x-y)/(x+y)-(x-3)]/(x+y)=[-1/(3+1)-0]/(3+1)=-1/16