## Calculus (3rd Edition)

$(0,1) \cup (1,\infty)$
The function $y=b^x$ is concave up when $y''$ is positive. We see that: $y''=b^x(\ln b)^2\ge0$ Note that for $b=1$, the graph is not concave up $(y''=0)$ because the graph is a straight line ($y=1^x=1$). Thus, $y$ is concave up for any value of $b$ except $1$: $(0,1) \cup (1,\infty)$