2( x2 +1/x2) - 9( x + 1/x) + 14 =
问题描述：
2( x2 +1/x2) - 9( x + 1/x) + 14 =
答
令a=x+1/x
a²=x²+2+1/x²
2(a²-2)-9a+14=0
(2a-5)(a-2)=0
x+1/x=5/2
2x²-5x+2=0
(2x-1)(x-2)=0
x=1/2,x=2
x+1/x=2
(x-1)²=0
x=1
x=1/2,x=2,x=1