True or False

a) The acute angle between 4i - 3j + k and 2i - k is 52, to the nearest degree. b) If a, b and c are positive integers and their hof(a, b, c) = 1, then the hef of ab and c is 1. c) If a, b, c are three integers such that ac|bc, then alb. d) For any vectors a and b y - X = la - b| = lal - |bl. e) If a, b E Z such that hef(a, 4) =hof(b, 4) = 2, then hof(a + b, 4) = 4. y - * = f) If alc and blc, then ablc