x-1/x=3两边平方可得x²-2+1/x²=9所以x²+1/x²=9+2=11
x^2+1/x^2=(x-1/x)^2+2=11
(x-1/x)^2=9x^2-2+1/x^2=9x^2+1/x^2=11
x-1=3xx=-0.5原式=1.25/0.25=5
