Find a Formula for the Slope of the Graph Of f

Multiple Choice

Find a formula for the slope of the graph of $f$ at the point $( x , f ( x ) )$ .Then use it to find the slope at the given point. $f ( x ) = \sqrt { x - 1 } , \quad ( 17,4 )$

A) $\begin{array} { l } m = - \frac { 1 } { 2 \sqrt { x - 1 } } \\\text { At } ( 17,4 ) , m = \frac { 1 } { 8 }\end{array}$
B) $\begin{array} { l } m = \frac { 1 } { 2 \sqrt { x - 1 } } \\\text { At } ( 17,4 ) , m = - \frac { 1 } { 8 }\end{array}$
C) $\begin{array} { l } m = \frac { 1 } { \sqrt { x - 1 } } \\\text { At } ( 17,4 ) , m = \frac { 1 } { 8 }\end{array}$
D) $\begin{array} { l } m = \frac { 1 } { 2 \sqrt { x - 1 } } \\\text { At } ( 17,4 ) , m = \frac { 1 } { 8 }\end{array}$
E) $\begin{array} { l } m = - \frac { 1 } { 2 \sqrt { x - 1 } } \\\text { At } ( 17,4 ) , m = - \frac { 1 } { 8 }\end{array}$