已知m^2+n^2-6m+10n+34=0求2m-3n的值
问题描述：
已知m^2+n^2-6m+10n+34=0求2m-3n的值
答
m^2+n^2-6m+10n+34=0
(m-3)^2+(n+5)^2=0
m-3=0 m=3
n+5=0 n= -5
2m-3n=21