Question 3. Let A, B, C D be four points such that AB = 2a, AC = −2a + 6b, AD = 3b. Prove that B, C and D are collinear. Question 4. Use De Moivre's Theorem to prove, sin 30 = 3 cos² € sin 3 cos² 0 sin 0 - sin³ 0 = 3 sin 0 - 4 sin³ 0.