Answer
Always
Work Step by Step
When both $a$ and $c$ are positive, the parabola opens upward and is above the $x$-axis, so there is no intersection with the $x$ axis and no solution.
Similarly, when both $a$ and $c$ are negative, the parabola opens downward and is below the $x$-axis, so there is no intersection with the $x$ axis and no solution.
Therefore the given statement is $\textit{always}$ true.
