∵m²-5m-1=0∴m-1/m=5∴(m-1/m)²=25∴m²+1/m²-2=25即m²+1/m²=27 由m²-5m-1=0得m²-1=5m先把m²-1=5m带入2m²-5m+1/m²得2m²-5m+1/m²=2m²-(m²-1)+1/m²=m²+1/m²+1=28
