已知m^2-5m-1=0,则2m^2-5m+1/m^2=?

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已知m^2-5m-1=0,则2m^2-5m+1/m^2=?
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已知m^2-5m-1=0,则2m^2-5m+1/m^2=?
已知m^2-5m-1=0,则2m^2-5m+1/m^2=?

已知m^2-5m-1=0,则2m^2-5m+1/m^2=?

答:
m²-5m-1=0,m²-5m=1
两边同除于m:
m-1/m=5
两边平方:
m²-2+1/m²=25
m²+1/m²=27
2m²-5m+1/m²
=m²-5m+m²+1/m²
=1+27
=28