Chapter 8 - Graphing Quadratic Functions - 8.1 - Graphing f(x) = ax^2 - Exercises - Page 424: 21

$f$ is increasing when $x>0$ $g$ is increasing when $x<0$

The graph of $f$ is a parabola which opens up, therefore $f$ is increasing at the right of the vertex, while the graph of $g$ is a parabola which opens down, therefore $g$ is increasing at the left of the vertex So $f$ is increasing when $x>0$ and $g$ is increasing when $x<0$.