What is the sum of the angles inside any triangle and how do I find a missing angle?

The three interior angles of any triangle always add up to 180 degrees, no matter the shape or size of the triangle. This is one of the most useful rules in geometry. To find a missing angle, add the two known angles and subtract from 180. Here the known angles are 50 and 60 degrees, so add them: 50 + 60 = 110. Now subtract from 180: 180 − 110 = 70. So the third angle is 70 degrees. You can check your work by adding all three: 50 + 60 + 70 = 180, which confirms it is correct. This angle-sum property works for every triangle, so whenever one angle is missing, this method finds it.