已知m²-5m-1=0,求2m²-5,+1/m²的值
问题描述：
已知m²-5m-1=0,求2m²-5,+1/m²的值
答
m^2-5m-1=0
m^2-5m=1
m^2-5m-1=0
m-5-1/m=0
m-1/m=5
m^2+1/m^2
=(m-1/m)^2+2
=5^2+2
=25+2
=27
2m^2-5m+1/m^2
=m^2-5m+m^2+1/m^2
=1+27
=28