Given `|veca|=|vecb|=1 and |veca + vecb|= sqrt3 "if" vecc` is a vector such that `vecc -veca - 2vecb = 3(veca xx vecb) ` then find the value of `vecc . Vecb`.

Explanation

To solve the problem step by step, we will follow the given conditions and use vector properties.

### Given:
1. \( |\vec{a}| = |\vec{b}| = 1 \)
2. \( |\vec{a} + \vec{b}| = \sqrt{3} \)
3. \( \vec{c} - \vec{a} - 2\vec{b} = 3(\vec{a} \times \vec{b}) \)

We need to find the value of \( \vec{c} \cdot \vec{b} \).
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