Question

In the diagram below, AB = BC, and mZA = 69º. Find mZBCD.

Answer 1

∠ BCD = 111°

Explanation:

Since AB = BC then the triangle is isosceles and the 2 base angles are congruent.

∠ ACB = ∠ A = 69°

∠ ACB and ∠ BCD are adjacent angles and sum to 180° , that is

∠ BCD + ∠ ACB = 180°

∠ BCD + 69° = 180° ( subtract 69° from both sides )

∠ BCD = 111°