Obtain linear approximation of the function

$f()=cos()$ one valid near

Obtain linear approximation of the function $f()=cos()$ one valid near $=\frac{}{3}$

$f()=cos(\frac{}{3})+sin(\frac{}{3})(+\frac{}{3})$

$f()=sin(\frac{}{3})-cos(\frac{}{3})(-\frac{}{3})$

$f()=cos(\frac{}{3})-sin(\frac{}{3})(-\frac{}{3})$

$f()=cos(\frac{}{3})+sin(\frac{}{3})(-\frac{}{3})$

$f()=cos(\frac{}{3})+sin(\frac{}{3})(+\frac{}{3})$

$f()=sin(\frac{}{3})-cos(\frac{}{3})(-\frac{}{3})$

$f()=cos(\frac{}{3})-sin(\frac{}{3})(-\frac{}{3})$

$f()=cos(\frac{}{3})+sin(\frac{}{3})(-\frac{}{3})$