`\ a b c` is an isosceles triangle with `A B=A Cdot` Side `B A`is produced to `D` such that `A B=A Ddot` Prove that `/_B C D` is a right angle.

Explanation

To prove that angle \( \angle BCD \) is a right angle in the given isosceles triangle \( ABC \) where \( AB = AC \) and \( AD = AB \), we can follow these steps:

### Step 1: Identify the Given Information
We know that:
- Triangle \( ABC \) is isosceles with \( AB = AC \).
- Side \( BA \) is extended to point \( D \) such that \( AB = AD \).

### Step 2: Establish Relationships Between the Sides
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