1. **Problem Statement:** We have three graphs of the form $f(x) = ax^2$ labeled $r$, $s$, and $t$. We need to identify which graphs correspond to $a > 0$ and which correspond to $a < 0$. 2. **Formula and Rules:** The general quadratic function is $f(x) = ax^2$. - If $a > 0$, the parabola opens upwards. - If $a < 0$, the parabola opens downwards. 3. **Analysis:** - Graphs $r$ and $s$ open upwards, so for these graphs, $a > 0$. - Graph $t$ opens downwards, so for this graph, $a < 0$. 4. **Final Answer:** - a) $a > 0$: Graphs $r$ and $s$ - b) $a < 0$: Graph $t$