✔ 最佳答案
設||x+2|-|2x-7||>=|3x-5|成立 則x之範圍?
Sol
x+2=0 =>x=-2
2x-7=0=>x=7/2
3x-5=0=>x=5/3
-──(-2)───(5/3)────(7/2)────
(1) x<-2
|x+2|=-x-2,|2x-7|=-2x+7,|3x-5|=-3x+5
|(-x-2)-(-2x+7)|>-3x+5
|x-9|>=-3x+5
9-x>=-3x+5
2x>=-4
x>=-2
無解
(2) -2<=x<=5/3
|x+2|=x+2,|2x-7|=-2x+7,|3x-5|=-3x+5
|(x+2)-(-2x+7)|>-3x+5
|3x-5|>=-3x+5
-3x+5>=-3x+5
-2<=x<=5/3………………….
(3) 5/3<=x<=7/2
|x+2|=x+2,|2x-7|=2x-7,|3x-5|=-3x+5
|(x+2)-(2x-7)|>-3x+5
|-x+9|>=-3x+5
9-x=-3x+5
2x>=-4
x>=-2
5/3<=x<=7/2……………….
(4) 7/2<x
|x+2|=x+2,|2x-7|=2x-7,|3x-5|=3x-5
|(x+2)-(2x-7)|>3x-5
|-x+9|>=3x-5
9-x=3x-5
14>4x
7/2>x
無解
綜合(1),(2),(3),(4)
-2<=x<=7/2