5. (19 points) Consider the equation 4cos23: 9cosa: 9 = 0. We want to nd all solutions with 27r 5 a: g 31r. (a) Show that all solutions of the equation satisfy cos a: = 0.75. (b) Using the following graph of cos 9;, show that there are ve solutions to the equa- tion. Label them #1 to #5 from left to right. (c) On the following unit circle, label points corresponding to all ve solutions. Also, label an angle whose size is arccos(O.75). (Note: points may have more than one label. Label each point with all relevant labels.) (d) Find all ve solutions. Write your answers to three decimal places