Question

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

Answer 1

Olá!

sen²(x) + cos²(x) = 1

(-12/13)² + cos²(x) = 1

144/169 + cos²(x) = 169/169

cos²(x) = (169 - 144)/169  

cos²(x) = 25/169  

cos(x) = -5/13