Question

se sen x= -12/13,com x no 3° quadrante , determine cos x

Answer 1

relacao fundamental da trigonometria
sen^2+cos^2=1
144/169+cos^2=1
cos^2=1-144/169
cos^2=169-144/169=25/169
$\cos = \sqrt{25 \div 169}$

cos=-5/13