18. \(4\) \(\sin(-\frac{3\pi}{2}) + \cos \frac{\pi}{4}\)

\(\sin(-\frac{3\pi}{2}) = 1\), \(\cos \frac{\pi}{4} = \frac{\sqrt{2}}{2}\), поэтому \(\sin(-\frac{3\pi}{2}) + \cos \frac{\pi}{4} = 1 + \frac{\sqrt{2}}{2}\).