If `vec(a) , vec(b) and vec(c )` be three vectors such that `vec(a) + vec(b) + vec(c )=0` and `|vec(a)|=3, |vec(b)|=5,|vec(C )|=7`, find the angle between `vec(a)` and `vec(b)`.

Explanation

To solve the problem, we need to find the angle between vectors \(\vec{a}\) and \(\vec{b}\) given the conditions that \(\vec{a} + \vec{b} + \vec{c} = 0\) and the magnitudes of the vectors are \(|\vec{a}| = 3\), \(|\vec{b}| = 5\), and \(|\vec{c}| = 7\).

### Step-by-Step Solution:

1. **Rearranging the Equation**:
Since \(\vec{a} + \vec{b} + \vec{c} = 0\), we can rearrange this to:
\[
\vec{a} + \vec{b} = -\vec{c}
...