Find the exact value of the expression. \( \sec \left(\frac{\pi}{4}\right)=\square \)

The value of \( \sec \left(\frac{\pi}{4}\right) \) can be found by recalling that secant is the reciprocal of cosine. Since \( \cos\left(\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2} \), we have: \[ \sec\left(\frac{\pi}{4}\right) = \frac{1}{\cos\left(\frac{\pi}{4}\right)} = \frac{1}{\frac{\sqrt{2}}{2}} = \frac{2}{\sqrt{2}} = \sqrt{2}. \] Thus, \( \sec \left(\frac{\pi}{4}\right) = \sqrt{2} \).