Question

the measure of an angle is 51°. what is the measure of its supplementary angle?

Explanation:

Step1: Recall supplement - angle formula

Let the angle be $\theta = 51^{\circ}$, and its supplementary angle be $\alpha$. The sum of an angle and its supplementary angle is $180^{\circ}$, so $\theta+\alpha = 180^{\circ}$.

Step2: Solve for the supplementary angle

$\alpha=180^{\circ}-\theta$. Substitute $\theta = 51^{\circ}$ into the formula, we get $\alpha = 180^{\circ}- 51^{\circ}=129^{\circ}$.

Answer:

$129^{\circ}$