Question

the measure of an angle is 51°. what is the measure of its supplement? 39° 49° 129° 139°

Explanation:

Step1: Recall supplement - angle definition

Two angles are supplementary if their sum is 180°. Let the given angle be $\alpha = 51^{\circ}$ and its supplement be $\beta$. Then $\alpha+\beta = 180^{\circ}$.

Step2: Solve for the supplement

We can find $\beta$ by rearranging the formula: $\beta=180^{\circ}-\alpha$. Substitute $\alpha = 51^{\circ}$ into the formula, so $\beta = 180^{\circ}-51^{\circ}=129^{\circ}$.

Answer:

C. 129°