已知：x^2+(1除以x^2)=18,则x-(1除以x)=
问题描述：
已知：x^2+(1除以x^2)=18,则x-(1除以x)=
答
x^2+(1除以x^2)=1+1/x^2=18,所以1/x^2=17,x^2=1/17,x=+-根号1/17
x-(1除以x)=（x^2-1）/x=（1/17-1）/+-根号1/17=正负（16*根号17）/17
答
x²+1/x²=18
x²-2+1/x²=16
(x-1/x)²=16
x-1/x=±4