f:[0,∞)→Rf : [0,\infty) \to \mathbb Rf:[0,∞)→R, f(0)=0f(0) = 0f(0)=0, f′′(x)>0f''(x) > 0f′′(x)>0 for x>0x > 0x>0. Then f(x)/xf(x)/xf(x)/x is
increasing in (0,∞)(0,\infty)(0,∞)
decreasing in (0,∞)(0,\infty)(0,∞)
increasing in (0,1](0,1](0,1] and decreasing in (1,∞)(1,\infty)(1,∞)
decreasing in (0,1](0,1](0,1] and increasing in (1,∞)(1,\infty)(1,∞)
