If `\ vec a\ a n d\ vec b` are two unit vectors inclined at an angle `theta` such that `|a+b|,1,` then `theta(2pi)/3` c. `pi/3

Explanation

To solve the problem, we need to analyze the given conditions about the unit vectors \(\vec{a}\) and \(\vec{b}\).

### Step-by-step Solution:

1. **Understanding the Given Information**:
- \(\vec{a}\) and \(\vec{b}\) are unit vectors, which means \(|\vec{a}| = 1\) and \(|\vec{b}| = 1\).
- The magnitude of the sum of these vectors is given as \(|\vec{a} + \vec{b}| < 1\).

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