The $3$rd degree Taylor polynomial for cos$($x$)$ centered at

a $=$

$2$

is given by$,$

cos$($x$)=$

x $$

$2$

$+$

$16$

$$

x $$

$2$

$3$

$+$ R$3($x$).$

Using this, estimate

cos$(81)$

correct to five decimal places.