f(x)=∣x-2∣ (x+1) ,f(x)= ∣2 x-1 ∣ -∣ x+1 ∣ 先写成分段函数的形式 再求出值域!
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f(x)=∣x-2∣ (x+1)

当x≥0时f(x)=(x-2)(x+1)=x^2-x-2=(x-1/2)^2-9/4≥-9/4

当x<0时f(x)=-(x-2)(x+1)=-(x-1/2)^2+9/4<2

f(x)= ∣2 x-1 ∣ -∣ x+1 ∣

当x≥1/2时 f(x)= (2 x-1 ) -( x+1 )=x-2则f(x)≥-3/2

当-1<x<1/2时 f(x)= -(2 x-1 ) -( x+1 )=-3x 则 -3/2< f(x)<3

当x<≤-1时 f(x)= -(2 x-1 ) +( x+1 )=-X+2 则f(x)≥3