If ` vec a+ vec b+ vec c= vec0,\ vec|a|=3,\ | vec b|=5\ a n d\ | vec c|=7`.
Find the angle betweeen ` vec a` and `vec b`

Explanation

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

### Given:
1. \(\vec{a} + \vec{b} + \vec{c} = \vec{0}\)
2. \(|\vec{a}| = 3\)
3. \(|\vec{b}| = 5\)
4. \(|\vec{c}| = 7\)

...