Find the measure of adjacent interior angle of a triangle, whose exterior angles is 80° 
Let measure of adjacent interior angle = x
And exterior angles = 80°
Now we know that "sum of an exterior angle of a triangle and its adjacent angle is equals to 180", so we get:
Exterior angle of a triangle + adjacent angle = 180°
Put the values of exterior angle and adjacent angle from above and we get:
x° + 80° = 180°
Subtraction 80°
x° = 100°
Hence, measure of adjacent interior angle = 100°

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Find the measure of adjacent interior angle of a triangle, whose exterior angles is 80° 
