The measures of two angles of a triangle are given below. find the measure of the third angle of the triangle in decimal form. 20.9°, 57.4°

The three angles of a triangle equal 180 degrees:
the first two angle are 20.9 and 57.4 which when added together equal: 20.9 + 57.4 = 78.3 degrees
 
 to find the 3rd angle subtract that total from 180:

180 - 78.3 = 101.7
 the 3rd angle is 101.7 degrees

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