Question

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

Explanation:

Step1: Recall supplementary - angle definition

Supplementary angles add up to 180°.
Let the given angle be $\alpha = 51^{\circ}$ and the supplementary angle be $\beta$.
We know that $\alpha+\beta = 180^{\circ}$.

Step2: Solve for the supplementary angle

$\beta=180^{\circ}-\alpha$.
Substitute $\alpha = 51^{\circ}$ into the formula: $\beta = 180 - 51$.
$\beta = 129^{\circ}$.

Answer:

$129$