Final answer:
The measure of the third angle of a triangle with two angles measuring 12° and 40° is 128°, calculated by subtracting the sum of the known angles from 180°. The correct answer is option: C. 128°.
Step-by-step explanation:
The sum of angles in a triangle is always 180 degrees. Given two angles of a triangle, we can find the third angle by subtracting the sum of the two known angles from 180. In this case, the two known angles are 12° and 40°.
Sum of known angles = 12° + 40° = 52°
Measure of the third angle = 180° - 52° = 128°
So, the correct answer is (C) 128°.