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In a Delta ABC, the sum of exterior angl...

In a `Delta ABC`, the sum of exterior angles at B and C is equal to:

A

`180^(@) - angle BAC`

B

`180^(@) + angle BAC`

C

`180^(@) - 2 angle BAC`

D

`180^(@) + 2 angle BAC`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question regarding the sum of the exterior angles at points B and C in triangle ABC, we can follow these steps: ### Step-by-Step Solution: 1. **Understanding Exterior Angles**: - In triangle ABC, when we extend the sides at points B and C, we create two exterior angles: one at point B (let's call it angle ABD) and one at point C (let's call it angle ACE). 2. **Applying the Exterior Angle Theorem**: - According to the exterior angle theorem, the exterior angle at a vertex of a triangle is equal to the sum of the two opposite interior angles. - Therefore, we have: - Angle ABD = Angle CAB + Angle ACB (for the exterior angle at B) - Angle ACE = Angle ABC + Angle CAB (for the exterior angle at C) 3. **Summing the Exterior Angles**: - Now, we can sum the two exterior angles: - Angle ABD + Angle ACE = (Angle CAB + Angle ACB) + (Angle ABC + Angle CAB) 4. **Simplifying the Expression**: - Combining the terms, we get: - Angle ABD + Angle ACE = Angle CAB + Angle ACB + Angle ABC + Angle CAB - This simplifies to: - Angle ABD + Angle ACE = 2 * Angle CAB + Angle ACB + Angle ABC 5. **Using the Angle Sum Property**: - The sum of the interior angles of triangle ABC is always 180 degrees: - Angle CAB + Angle ABC + Angle ACB = 180 degrees 6. **Final Calculation**: - Substituting the sum of the interior angles into our equation: - Angle ABD + Angle ACE = 180 degrees + Angle CAB - Therefore, the sum of the exterior angles at B and C is equal to: - Angle ABD + Angle ACE = 180 degrees + Angle B 7. **Conclusion**: - Hence, the sum of the exterior angles at B and C is equal to 180 degrees plus the angle at B. ### Final Answer: The sum of the exterior angles at B and C is equal to \(180^\circ + \text{Angle B}\). ---
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