2022 · Q79
In a triangle ABC, AB = AC and BC is produced to D such that ∠ACD = x, then what is ∠BAC equal to?
Elementary MathematicsGeometry: Lines, Angles and Triangles
- A2x - 90°
- B2x - 180°
- C180° - 2x
- Dx/2
Explanation
Exterior ∠ACD = x equals the sum of the remote interiors: x = ∠BAC+∠ABC. With AB = AC, ∠ABC = ∠ACB = 180°-x, so ∠BAC = x-(180°-x) = 2x-180°. Hence the keyed option is B.