In triangle ABC, AB = BC. If ∠ABC = 40°, find the value of ∠BAC.
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Worked Solution
Triangle ABC is an isosceles triangle because AB = BC.
In an isosceles triangle, the base angles are equal. So, ∠BAC = ∠BCA.
The sum of angles in a triangle is 180°.
∠BAC + ∠BCA = 180° - 40° = 140°.
Since ∠BAC = ∠BCA, ∠BAC = 140° ÷ 2 = 70°.
Key formula: Base angles of isosceles triangle are equal.; Sum of angles in a triangle = 180°.
Answer: 70°
Correct answer: 70°
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