一元二次不等式的因式分解怎么解

Question

比如像x^2-2x-3<=0

Answer 1

一元二次不等式的因式分解
x^2-2x-3<=0

<==>
(x+1)(x-3)≤0
<==>
{x+1≤0 或 {x+1≥0
{x-3≥0 ｛x-3≤0
<==>
{x≤-1 或 {x≥-1
{x≥3 {x≤3
<==>
x∈空集或-1≤x≤3
<==>
-1≤x≤3

举例2
x^2-2x-3>0

<==>
(x+1)(x-3)>0
<==>
{x+1>0 或 {x+1<0
{x-3>0 ｛x-3<0
<==>
{x>-1 或 {x<-1
{x>3 {x<3
<==>
x>3或x<-1

Answer 2

就穿针引线法