Answer:
20°
Explanation:
You want to know the measure of angle 'a' in a triangle with exterior angle 58.5° and remote interior angles of 38.5° and 'a'.
Exterior angle theorem
The exterior angle theorem provides a shortcut solution to problems like this one. It tells you the exterior angle (58.5°) is the sum of the remote interior angles (38.5°, a).
58.5° = 38.5° +a
20° = a . . . . . . . . . . subtract 38.5°
The value of a is 20°.
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