Question

two angles of a triangle measure 12° and 40°. what is the measure of the third angle of the triangle? a. 38° b. 48° c. 128° d. 308°

Explanation:

Step1: Recall angle - sum property

The sum of the interior angles of a triangle is $180^{\circ}$. Let the three angles of the triangle be $A$, $B$, and $C$. So $A + B+C=180^{\circ}$.

Step2: Identify known angles

We know that $A = 12^{\circ}$ and $B = 40^{\circ}$.

Step3: Calculate the third - angle

We can find $C$ by the formula $C=180^{\circ}-(A + B)$. Substitute $A = 12^{\circ}$ and $B = 40^{\circ}$ into the formula: $C=180-(12 + 40)=180 - 52=128^{\circ}$.

Answer:

C. $128^{\circ}$