(b) Prove that if an E R \ {O} and lan+danl -+ r as n -+ 00, for some r > 0, then lanl1/ n -+ r as n -+ 00.

*10. Let x ::; y be any pair of extended real numbers. Prove that if L%"=l ak is conditionally convergent, then there is a rearrangement L;:l bj of L%:l ak whose partial sums Sn satisfy liminf Sn = x and limsupsn = y.