Find the angle between two `veca` and `vecb` with magnitudes 1 and 2 respectively and when `veca.vecb=1`.

Explanation

To find the angle between two vectors \(\vec{a}\) and \(\vec{b}\) given their magnitudes and their dot product, we can follow these steps:

### Step 1: Write down the given information
We know:
- Magnitude of \(\vec{a}\): \(|\vec{a}| = 1\)
- Magnitude of \(\vec{b}\): \(|\vec{b}| = 2\)
- Dot product: \(\vec{a} \cdot \vec{b} = 1\)

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