Answer
(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.
