x^2-3x-1=0,求x^2+1/x^2的值
问题描述：
x^2-3x-1=0,求x^2+1/x^2的值
答
x^2-3x-1=0
两边除以X
x-3-1/x=0
x-1/x=3
(x-1/x)²=9
x^2+1/x^2-2=9
x^2+1/x^2=9+2=11
答
x^2-3x-1=0
x^2-1=3x
两边平方
x^4-2x^2+1=9x^2
x^4+1=11x^2
两边除以x^2
x^2+1/x^2=11