Question

已知:3m^2+2mn-n^2=0,m≠0,n≠0,化简:(3m^2-5mn+n^2)/(m^2-n^2)

不要复制答案

Answer 1

3m^2+2mn-n^2=0
1 1
3 -1
（m+n)(3m-n)=0
∴m+n=0(不合题意，舍去）或3m-n=0
∴n=3m

(3m^2-5mn+n^2)/(m^2-n^2)
=(3m²-5m×3m+9m²)÷﹙m²-9m²)
=(-3)÷(-8)
=3/8

追问

为什么m+n=0要舍去

追答

分母m²-n²≠0