5x-2y=5
x-4y=1
x=1 y=0
mx+5y=4
m=4
5x+ny=1
n =无解
5x-2y=23
x-4y=1
x=5 y=1
mx+5y=4
5m+5=4
m=-1/5
5x+ny=1
25+n=1
n =-24