\(z = 3\left( {\cos \left( { - \dfrac{\pi }{3}} \right) + i\sin \left( { - \dfrac{\pi }{3}} \right)} \right)\)

\(z = 3\left( {\cos \left( { - \dfrac{\pi }{3}} \right) - i\sin \left( { - \dfrac{\pi }{3}} \right)} \right)\) 

\(z = 3\left( { - \cos \dfrac{\pi }{3} - i\sin \dfrac{\pi }{3}} \right)\)   

\(z = 3\left( {\cos \dfrac{\pi }{3} + i\sin \dfrac{\pi }{3}} \right)\)