(m-1/m)²=9m²-2+1/m²=9m²+2+1/m²=13(m+1/m)²=13m+1/m= ± √13m²-1/m²=(m-1/m)(m+1/m)=3*(± √13)= ±3√13
先求m=-0.5则所求值为1.5
