(a) $x \in (-\infty,0)$ (b) Nowhere ($\varnothing$) (c) $x \in (0,\infty)$ (d) Nowhere ($\varnothing$)
Work Step by Step
The function is always increasing for all $x$, so (b) and (d) are both "for no x". The rate of change is becoming more positive when x is positive, so that region is concave up. The rate of change is becoming less positive when x is negative, so that region must be concave up.