# An exterior angle of a triangle is 120° and one of the interior opposite angles is 30°. Find the other angles of the triangle.

Given: exterior angle let ABD = 120°

One interior angle let BAC = 30°

As we know, using theorem (2) i.e. if a side of the triangle is produced, the exterior angle so formed is equal to the sum of corresponding opposite interior angles.

Hence,

ABD = BAC + BCA

120° = 30° + BCA

BCA = 120° - 30°

BCA = x = 90°

As we know, using theorem (1), in any triangle, sum of the three interior angles is 180°.

So,

BAC + BCA + ABC = 180°

30° + 90° + y = 180°

y = 180° - 30° - 90°

y = 60°

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