Explanation:
All sides in a triangle is equal to 180°
So whenever given two sides only, add them up, and subtract from 180. That will give you the missing sides length.
So 23 + 84 = 107
180 - 107 = 73
The missing side of the triangle is equal to 73°.
110 + 42 = 152
152 - 180 = 28°
The missing side of the triangle is equal to 28°.
Another example is:
100°, 40°
Front the missing side in this triangle.
100 + 40 = 140°
180 - 140 = 40°
The missing length is 40°