Question 11 - 8 marks You should be able to answer this question after studying Unit 12. (a) Use Euler's formula eid = cos 0 + i sin 0 to obtain the trigonometric identities sin(a + 3) = sin a cos B + cos a sin B cos(a + B) = cos a cos B - sin a sin B. [5] (Hint: consider eideiB.) (b) By first writing i in exponential form, find a in Cartesian form, correct to four decimal places. (Note that the rules for indices in Unit 1 of Book A still apply to complex numbers.) [3]