If `veca +vecb +vecc=0, |veca|=3,|vecb|=5, |vecc|=7` , then find the angle between `veca and vecb`.

Explanation

To find the angle between the vectors \( \vec{a} \) and \( \vec{b} \) given that \( \vec{a} + \vec{b} + \vec{c} = 0 \), \( |\vec{a}| = 3 \), \( |\vec{b}| = 5 \), and \( |\vec{c}| = 7 \), we can follow these steps:

### Step 1: Rewrite the equation
From the equation \( \vec{a} + \vec{b} + \vec{c} = 0 \), we can rearrange it to express \( \vec{c} \) in terms of \( \vec{a} \) and \( \vec{b} \):
\[ \vec{c} = -(\vec{a} + \vec{b}) \]

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