Question

De acordo com o estudo do seno e cosseno de ângulos obtusos, qual o cosseno do ângulo de 150º?

Answer 1

$\cos(150^{\circ})\\ \\ =\cos(180^{\circ}-30^{\circ})\\ \\ =-\cos(30^{\circ})\\ \\ =-\dfrac{\sqrt{3}}{2}.$