A) A right triangle has one angle that measures \( 80^{\circ} \). What is the measure of the other acute angle?

In a right triangle, the sum of the angles must always equal \( 180^{\circ} \). Since one angle is a right angle (\( 90^{\circ} \)) and you're given one acute angle of \( 80^{\circ} \), you can find the other acute angle by subtracting the sum of these two angles from \( 180^{\circ} \). So, the calculation goes: \( 180^{\circ} - 90^{\circ} - 80^{\circ} = 10^{\circ} \). Therefore, the measure of the other acute angle is \( 10^{\circ} \). A common mistake when working with right triangles is to forget that the right angle is already \( 90^{\circ} \), leading to confusion about how to calculate the remaining angles. Always remember that the sum of angles in any triangle is \( 180^{\circ} \), and that \( 90^{\circ} \) is already allocated to the right angle.