(1)x^2-2x-3≤0
(x-3)(x+1)≤0
-1≤x≤3
(2)-x^2+4x-5<0
x^2-4x+5>0
x^2-4x+4+1>0
(x-2)^2+1>0
x是全体实数
(3)-x^2+6x-10>0
x^2-6x+10