9. The first three terms of a geometric series are sin cos 0 and 0.5 where is a constant (a) Show that 2sin20+ sin 0-2 = 0 Given that lies in the interval 90 < < 180 (b) find the value of 6 giving your answer to one decimal place. (c) Hence prove that this series is convergent. (d) Find, to two significant figures, S