x+ 1/x =3两边平方得：(x+1/x)²=9x²+1/x²+2=9两边同减去4得：x²+1/x²-2=5(x-1/x)²=5x-1/x=±√5
x+ 1/x =3(x- 1/x)²=(x+1/x)²-4=9-4=5所以 x-1/x=±√5
x+ 1/x =3 3x=x+1 3x-x=1 2x=1 x=1/2 x-1/x=1/2-1/1/2= -1/2
