已知不等式l ax+1 l小于等于b的解集是[-1,3],求a,b的值

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lax+1l≤b
-b≤ax+1≤b
-b-1≤ax≤b-1
(1)a＞0时
-(b+1)/a≤x≤(b-1)/a
-(b+1)/a=-1
(b-1)/a=3
b=-2,a=-1不满足假设 舍
(2)a=0时
-b不满足题意 舍
(3)a(b-1)/a≤x≤-(b+1)/a
-(b+1)/a=3
(b-1)/a=-1
b=2 a=-1