m²-4m+4+|n+1|=0
(m-2)²+|n+1|=0
m-2=0n+1=0
m=2 n=-1
[（n/m）-（m-n）]/（m-n）
=[(-1/2)-(2-(-1))]/(2-(-1))
=[-1/2-3]/3
=-7/2/3
=-7/6