本題的g(x)題意不清,現(xiàn)分兩種情況解答如下：
Case 1：g(x) = 1 + a/x
df/dx = -1 + 2a
let df/dx < 0, we geta < 1/2
dg/dx = -a/x²
let dg/dx < 0, we obtain a > 0
So, ans is1 ≤a < 1/2
Case 2 : g(x) = a/(x+1)
df/dx = -1 + 2a
let df/dx < 0, we geta < 1/2
dg/dx = -a/(x+1)²
let dg/dx < 0, we obtain a > 0
So, ans is also 1 ≤a < 1/2.