To determine the measure of the third angle in a triangle when two angles are given, remember that the sum of all three angles in any triangle always equals 180°. This principle is a fundamental property of triangles.
Here are the given angles:
- First angle: 25°
- Second angle: 55°
Let's find the measure of the third angle step-by-step:
1. Write down the sum of all angles in a triangle:
[tex]\[
\text{Sum of the angles in a triangle} = 180°
\][/tex]
2. Add the measures of the two given angles:
[tex]\[
25° + 55° = 80°
\][/tex]
3. Subtract the sum of the two given angles from the total sum of the angles in the triangle:
[tex]\[
180° - 80° = 100°
\][/tex]
So, the measure of the third angle is:
[tex]\[
100°
\][/tex]
Therefore, the correct option is:
- B. 100°
