Let a and b be real numbers. Find the maximum value of \(a \cos \theta + b \sin \theta\) in terms of a and b.
\(a \cos(\theta) + b \sin(\theta) = \\ \sqrt{a^2 + b^2}\sin(\theta + \phi),~\phi = \tan^{-1}\left(b,a\right)\\ -1 \leq \sin(\theta+\phi) \leq 1\\ \text{The max value is thus $\sqrt{a^2+b^2}$}\)
