Advanced Mathematics Primary 5 Geometry

In triangle ABC, angle A = 62° and angle B = 47°. The side BC is extended to a point D. Find angle ACD.

A 109°
B 71°
C 118°
D 133°
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Worked Solution

Step 1: Recall the Exterior Angle Theorem. The exterior angle of a triangle equals the sum of the two non-adjacent (remote) interior angles. Step 2: Identify the remote interior angles for angle ACD. The exterior angle ACD is formed at vertex C by extending BC to D. The two remote interior angles are angle A = 62° and angle B = 47°. Step 3: Apply the theorem. Angle ACD = angle A + angle B = 62° + 47° = 109° Verification: Interior angle C = 180° − 62° − 47° = 71°. Angle ACD = 180° − 71° = 109° ✓ Answer: 109° Answer: 109°

Correct answer: 109°

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