dominicsavio Posted September 14, 2007 Share Posted September 14, 2007 The sequence a1, a2, a3....a(n) of n integers is such that a(k) = k if k is odd a(k) = -a(k-1) is k is even Is the sum of the terms in the sequence positive? (1) n is odd (2) a(n) is positive Please post explanation OA=D Quote Link to comment Share on other sites More sharing options...
krusta80 Posted September 14, 2007 Share Posted September 14, 2007 The sequence a1, a2, a3....a(n) of n integers is such that a(k) = k if k is odd a(k) = -a(k-1) is k is even Is the sum of the terms in the sequence positive? (1) n is odd (2) a(n) is positive Please post explanation OA=D (1) n is odd If n is odd: sum(a(k)) = (k_1 - k_1) + (k_3 - k_3) + ... + (k_n-2 - k_n-2) + k_n = k_n SUFFICIENT, since any every sequence starts with 1 and each off term equals its index, including k_n. (2) a(n) is positive If a(n) is positive, then n has to be odd. SUFFICIENT D Quote Link to comment Share on other sites More sharing options...
nikiforos Posted September 14, 2007 Share Posted September 14, 2007 Another vote for D Pls post the OA Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.