Question

An exterior angle of a triangle is 120º and one of its interior opposite angles is 40º. Then find the other two angles in degree​

Answer 1

According to the exterior angke theorem, the exterior angle of a triangle is equal to the sum of two opposite interior angles.

As one of the interior angle is 40°

So the other angle = Exterior angle - First interior angle = 120°- 40° = 80°

We know that sum of all angles of a triangle is 180°

As 1st angle = 40°

And 2nd angle = 80°

Thus , 3rd angle = 180° - [1st angle + 2nd angle]

Sum of 1st and 2nd angle is the exterior angle i.e., 120°

So, 3rd angle = 180° - 120° = 60°

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