Question 3 Find all values of r in the interval [0, 27] that satisfy cos(21) + cos(I) = 0. Hint: cos(2r) = 2 cos (I) - 1. (4 mar Question 4 : Application Problem 1 Suppose V(t) = 5 - cos represents the volume (in litres) of air in a person's lungs t seconds after a full exhale. (a) Use the CAST RULE to find V () . Draw your reference angle and express your answer both in exact form and rounded to one decimal place. Intepret your result in the context of the question. (3 marks) (b) Within a single breathing cycle (i.e., assuming t E [0, 3.5]), when does a person have 9 of a litre of air in their lungs? Express your answer(s) in exact form without using a calculator. (4 marks)