What is the sum of the angles in a triangle?

• A. 90°
• B. 180°
• C. 360°
• D. 270°

Answer: (B)

In any triangle, regardless of the type (whether it is acute, obtuse, or right), the sum of all internal angles is always 180 degrees. This fundamental property is based on Euclidean geometry, which describes the geometry of flat surfaces.

To understand why the sum is 180 degrees, you can visualize or construct a triangle and draw a line parallel to one of the triangle's sides through the opposite vertex. The angles that are formed on either side of the triangle will correspond to the triangle's internal angles and will illustrate that these angles combine to equal 180 degrees.

Therefore, knowing that the sum of the angles in a triangle is consistently 180 degrees is essential in various mathematical applications, including solving for unknown angles and proving other properties in geometry.