Question

${tan}^{- 1} (1) =$

\begin{aligned} We know that tan (\frac{π}{4}) & = & 1 \\ then, \frac{π}{4} & = & {tan}^{- 1} (1) \\ Hence, {tan}^{- 1} (1) & = & \frac{π}{4} \end{aligned}

So, correct answer is option-1, $\to \frac{π}{4}$