For the curve:

$f(x)=\sqrt[\phantom{2}]{x-5}$

the equation of the tangent line when $x=9$ is

$y=\frac{1}{4}(x+1)$

$y=-\frac{1}{4}(x+1)$

$y=\frac{1}{4}(x-1)$

$y=-\frac{1}{4}(x-1)$