2. (a) Show that cos 20 cos 40 cos 80 (4 marks) (b) If A, B and C are angles in AABC, show that i. tan A + tan B + tan C = tan A tan B tan C (4 marks) ii. sin 2 A + sin 2 B + sin 2 C = 4 sin A sin B sin C (4 marks) sin (n + 7) 20 (c) Show that 1 + 2 cos x + 2 cos 2x + 2 cos 3x + . . . + 2 cosnx = (4 marks) sin - x