Please help me with 1st sum 
1. Let f be an injective function with domain [a, b] and range [c, d]. If $\text{α}$ is a point in (a, b) such that f has left hand derivative l  and 
right hand derivative r at x =  $\text{α}$  with both l and r non-zero different and negative, then left hand derivative
right hand derivative of f^-1  at x = f( $\text{α}$ ) respectively, is 
$$\begin{gathered} \text{(A) }\frac{1}{\text{r}}\text{,}\frac{1}{\text{l}} \\ \text{ (B) r , l} \\ \text{ (C) }\frac{1}{\text{l}}\text{,}\frac{1}{\text{r}} \\ \text{(D) l, r} \end{gathered}$$