x²-x-1≠0 配方
[x²-x+(1/2)²]-1-(1/2)²≠0
(x-1/2)²≠1+1/4
(x-1/2)²≠5/4
x-1≠±√(5/4)
x-1≠±√5/2
x-1≠√5/2且x-1≠-√5/2
x≠1+√5/2且x≠1-√5/2