Standard Mathematics Primary 5 Geometry

In triangle ABC, AB = BC. If ∠ABC = 40°, find the value of ∠BAC.

A 70°
B 100°
C 140°
D 40°
Show Worked Solution

Worked Solution

Step 1: Triangle ABC is an isosceles triangle because AB = BC. Step 2: In an isosceles triangle, the base angles are equal. So, ∠BAC = ∠BCA. Step 3: The sum of angles in a triangle is 180°. Step 4: ∠BAC + ∠BCA = 180° - 40° = 140°. Step 5: Since ∠BAC = ∠BCA, ∠BAC = 140° ÷ 2 = 70°. Answer: 70°

Correct answer: 70°

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