An exterior angle of a triangle is 115° and one of the

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An exterior angle of a triangle is 115° and one of the interior opposite angles is 45°. Then the other two angles are

1. 65°, 70°
2. 60°, 75°
3. 45°, 90°
4. 50°, 85°

Correct Option: A

The exterior angle of a triangle is equal to the sum of two remaining opposite angles.

Given that , ∠ACD = 115° and ∠A = 45°
we know that , ∠ACD = ∠A + ∠B
⇒ 115° = 45° + ∠B
⇒ ∠B = 115° – 45° = 70°
⇒ ∠ACB = 180° – 115° = 65°
OR
∠ACB = 180° – ∠ACD
∠ACB = 180° – 115° = 65°
∴ ∠B = 180° – 65° – 45° = 70°