f(x)=√(-x^2+5x-4)+1/(x-2)
定义域是：-x^2+5x-4≥0,且x-2≠0
===> x^2-5x+4≤0,且x≠2
===> (x-1)(x-4)≤0且x≠2
===> 1≤x≤4,且x≠2