a) z = 8 ( cos 210° + i sen210°)
30° Angulos correspondentes: 150°, 210° , 330°
210° está no 3° quadrante, logo o seno e cosseno serão negativos
sen 210° = [tex] \frac{-1}{2} [/tex] e cos 210° = [tex] \frac{- \sqrt{3} }{2} [/tex]
z = 8 [tex]( \frac{- \sqrt{3} }{2} + i \frac{-1}{2} )[/tex]
z = 8.[tex] \frac{- \sqrt{3} }{2} [/tex] + 8.i.[tex] \frac{-1}{2} [/tex]
z = -4√3 - 4i
b) z= 5 (cos60° + i sen 60°)
cos 60° = [tex] \frac{1}{2} [/tex] e sen 60° = [tex] \frac{ \sqrt{3} }{2} [/tex]
[tex]5. \frac{1}{2} + 5.i. \frac{ \sqrt{3} }{2} [/tex]
[tex] \frac{5 + 5.i. \sqrt{3} }{2} [/tex]