Chapter 8 - Application of Trigonometry - Chapter 8 Test Prep - Review Exercises - Page 841: 66

$$3i$$

$$\eqalign{ & {\text{Trigonometric form }}3\left( {\cos 90^\circ + i\sin 90^\circ } \right) \cr & {\text{Calculate }}\cos 90^\circ {\text{ and }}\sin 90^\circ \cr & \cos 90^\circ = 0 \cr & \sin 90^\circ = 1 \cr & {\text{,then}} \cr & 3\left( {\cos 90^\circ + i\sin 90^\circ } \right) = 3\left( {0 + i} \right) \cr & = 3i \cr} $$