Evaluating at \(\frac{\pi}{4}\)}
Know standard values: \( \cos \left( \frac{\pi}{4} \right) = \frac{1}{\sqrt{2}} \)
For high even powers, use \( \left( \frac{1}{\sqrt{2}} \right)^{2n} = 2^{-n} \)
Focus on power expressions when constant terms dominate