Question

Let $f\left(x\right)=se{c}^{-1}x+ta{n}^{-1}x$. Then f(x) is real for

• A.
  
• B.
  
• C.
  
• D. None of these

Answer 1

The correct option is C

$se{c}^{-1}x$ is real when x $\le$ -1 or x $\ge$ 1
$ta{n}^{-1}x$ exists for all x $ϵ$ R
$\Rightarrow xϵ(-\infty ,-1]\cup [1,+\infty )$