若0若0
若0(x+1/x)²=6²x²+2+1/x²=36x²+1/x²=34(x-1/x)²=x²-2+1/x²=34-2=320
0x-1/x<0x-1/x=-√[(x+1/x)^2-4]=-√(36-4)=-4√2