Vector Algebra

Let \(\overrightarrow a\), \(\overrightarrow b\), \(\overrightarrow c\) be three mutually perpendicular vectors of the same magnitude and equally inclined at an angle \(\theta\), with the vector \(\overrightarrow a\) + \(\overrightarrow b\) + \(\overrightarrow c\). Then 36cos²2\(\theta\) is equal to ___________.