# Question #23847

$\frac{\sqrt{2}}{2} + 3$
Let $f \left(x\right) = \cos \left(x\right) + 3$.
We know that $\cos \left(\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2}$, which is a value that should definitely be memorized.
So $f \left(\frac{\pi}{4}\right) = \cos \left(\frac{\pi}{4}\right) + 3 = \frac{\sqrt{2}}{2} + 3$