What is the value of \(\tan(\tan^{-1}x)\)?

Correct answer: \(x\)

The angle \(\tan^{-1}x\) (principal value of arctan) has tangent equal to \(x\). Since arctan takes values in \((-\tfrac{\pi}{2},\tfrac{\pi}{2})\) where \(\tan\) is one-to-one, the composition gives \(\tan(\tan^{-1}x)=x\) for all real \(x\). Option B (0) holds only when \(x=0\); option C (\(1/x\)) and D (\(-x\)) are true only for special values and are not generally correct. Exam tip: remember the principal range of \(\tan^{-1}x\) so you can use the identity \(f(f^{-1}(x))=x\) when \(f\) is one-to-one on that range.