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Re: don't know how to crack [#permalink]
01 Mar 2011, 00:18
Hi, If you try to group the terms then you will see the solution. [(-1)^m]*[(-1)^n+(1)]+[(-1)^n]
From A we know that m is odd so the sign will be neg. So no matter what the sign of n is the ans is -1. from b we know that n is odd which means that the sign is neg. The term in the  is 0, and the ans is -1.