Q)
If \( \overrightarrow a + \overrightarrow b + \overrightarrow c = 0\) and \( | \overrightarrow a | = 3, | \overrightarrow b | = 5\) and \( |\overrightarrow c | = 7\), show that the angle between \( \overrightarrow a\: and \: \overrightarrow b \) is equal to \( 60^{\circ}\)
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