解：
x-1/x=3乘以x得x²-1=3xx²-3x-1=0x²-3x=14-1/2x²+3/2x
=-1/2(x²-3x-8)
=-1/2*(1-8)
=7/2
x-1/x =3，两边同乘以xx²-1=3xx²-3x=14-1/2x²+3/2x=-1/2(x²-3x-8)=-1/2(1-8)=7/2
