# A is an acute angle and cos A=5/13. Without using multiplication or calculator,find the value of each of the following trigonometry function a) cos (180°-A) b) sin (180°-A) c) tan (180°+A) ?

$\cos \left(180 - A\right) = - \cos A = - \frac{5}{13}$
$\sin \left(180 - A\right) = \sin A = \sqrt{1 - {\cos}^{2} A} = \frac{12}{13}$
$\tan \left(180 + A\right) = \sin \frac{180 + A}{\cos} \left(180 + A\right) = \frac{- \sin A}{- \cos A} = \tan A = \frac{12}{5}$