Question

Calcule os senos e cossenos seguindo o modelo
abaixo:

a) cos210° =?

210° está no 3° quadrante (cosseno é negativo)

180° + α = 210°
α = 30°
cos210° = −cos30° = −√3/2

b)cos120° =
c) sen210° =
d)cos300° =
e)sen330° =
f) cos135° =
g) cos240° =
h)sen240° =
i) cos225° =

Answer 1

b)cos120° =-cos(180°-120°)=-cos60°=$\mathsf{-\dfrac{1}{2}}$

c) sen210° =-sen(210°-180°)=-sen30°=$\mathsf{-\dfrac{1}{2}}$

d)cos300° =cos(360°-300)=cos60°=$\mathsf{\dfrac{1}{2}}$

e)sen330° =-sen(360-330)=-sen30°=$\mathsf{-\dfrac{1}{2}}$

f) cos135° =-cos(180°-135°)=-cos45°=$\mathsf{-\dfrac{1}{2}}$

g) cos240°=-cos(240°-180°)=-cos(60°)=$\mathsf{-\dfrac{1}{2}}$

h)sen240° =-sen(240°-180°)=-sen(60°)=$\mathsf{-\dfrac{\sqrt{3}}{2}}$

i) cos225°= cos(225°-180°)=-sen45°=$\mathsf{-\dfrac{\sqrt{2}}{2}}$