The third angle of a triangle is equal to 180 degrees minus (the sum of the first two angles).
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55°
The missing angle measure is 100 degrees.
77. The sum of the three angles in a triangle equal the sum of 180 degrees
The sum of the angles is 180 degrees in any triangle. So 180-140 is 40 and the third angle is 40 degrees.
The sum of two complementary angles is 90 degrees. The three angles of a triangle add up to 180 degrees. Hence, if you subtract the complementary angles from 180, you have the measure of the third angle: 180 - 90 = 90 (this is the third angle) As a rule, if two angles of a triangle are complementary, the third angle is a right angle (90 deg). The three angles together form a right triangle.