If \(f(x)=\sqrt{x+2}+\sqrt{8-x}\), what is the maximum value of \(f\)?

Correct answer: \(2\sqrt{5}\)

For real values, \(x+2\ge 0\) and \(8-x\ge 0\), so the domain is \(-2\le x\le 8\). By the Cauchy–Schwarz inequality, \((\sqrt{x+2}+\sqrt{8-x})^2\le 2[(x+2)+(8-x)]=20\). Hence \(f(x)\le 2\sqrt{5}\). Equality occurs when \(\sqrt{x+2}=\sqrt{8-x}\), which gives \(x=3\). Therefore, the maximum value is \(2\sqrt{5}\). Exam tip: first determine the domain of radical expressions, then check the equality condition for the inequality used.