In a ` A B C ,` if `A B=A C\ a n d\ B C` is produced to `D` such that `/_A C D=100^0,` then `/_A=` `20^0` (b) `40^0` (c) `60^0` (d) `80^0`

Explanation

To solve the problem step by step, we will analyze the given information and use properties of triangles.

### Step 1: Understand the Given Information
We have a triangle \( ABC \) where \( AB = AC \) and \( BC \) is extended to point \( D \) such that \( \angle ACD = 100^\circ \).

### Step 2: Identify the Angles
Since \( AB = AC \), triangle \( ABC \) is an isosceles triangle. This means that the angles opposite the equal sides are also equal. Therefore, we can denote:
- \( \angle B = x \)
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