Field and Wave Electromagnetics 2nd Edition by David Cheng

Exercise 2

Unit vectors a A and a B denote the directions •of two-dimensional vectors A and B that make angles and , respectively, with a reference x-axis, as shown in Fig.
a) Obtain a formula for the expansion of the cosine of the difference of two angles, cos ( - ) , by taking the scalar product a A • a B. b) Obtain a formula for sin ( - ).
Figure: Graph