6. a) Consider the following system r(s). K(s+2) (s+1)(s+4)(s-1) [10] (s). Find the range of K for which there will be only two closed-loop poles on the right-half of the s-plane. b) For each of the figure shown below, state whether or not the sketch is a valid root locus. Justify your answer. (i) jw (ii) (iii) (iv) jw jw jw [10]