先化简,再求值2x-6y/x^2-9y^2,已知2x+6y+1=0

题目

先化简,再求值2x-6y/x^2-9y^2,已知2x+6y+1=0

答案

2x+6y+1=0
x+3y=-1/2
2x-6y/x^2-9y^2
=2(x-3y)/(x+3y)(x-3y)
=2/(x+3y)
=2/(-1/2)
=--4