To reflect a point (x, y) across the x-axis, we keep the x-coordinate the same and change the sign of the y-coordinate.
For the point (5, -8), when we reflect it across the x-axis, the x-coordinate remains the same (5), but the sign of the y-coordinate becomes positive.
Therefore, the reflection of the point (5, -8) across the x-axis is (-5, 8).