If a triangle has angles measuring 45° and 55°, what is the measure of the third angle?

• A. 70°
• B. 80°
• C. 90°
• D. 100°

Answer: (B)

To determine the measure of the third angle in a triangle when two angles are already given, you can use the triangle sum property. This property states that the sum of the interior angles in any triangle must always equal 180 degrees.

In this case, you already have two angles: 45° and 55°. First, you'll add these two angles together:

45° + 55° = 100°

Next, to find the measure of the third angle, you subtract the sum of the two known angles from 180°:

180° - 100° = 80°

Thus, the measure of the third angle is 80°. This confirms that the correct answer is indeed accurate, as 80° is the remaining angle needed to complete the triangle, maintaining the total of 180°.