Jen Posted September 21, 2014 Report Share Posted September 21, 2014 Hey! I need help to finish my maths problem. I've already read some guidelines to solve this problem, but I really don't understand. Please just tell me how to solve it, but it would be really nice if it's fully detailed. I'm really bad at following if there's no explanation.. The sum, Sn, of the first n terms of a geometric sequence, whose nth term is un, is given by Sn = {7^(n -1) -a^}/7^n , where a > 0. (a) Find an expression for un. (b) Find the first term and common ratio of the sequence. Consider the sum to infinity of the sequence. (i) Determine the values of a such that the sum to infinity exists. (ii) Find the sum to infinity when it exists. Thanks in advance! Reply Link to post Share on other sites More sharing options...
SYL Posted September 23, 2014 Report Share Posted September 23, 2014 What is the exponent next to a? Since its been replaced by a thumbs down hahah..Anyway I'll tell you tips on each of the questions. For (a), just use the fact that un = Sn - Sn-1 (b) Substitute n = 1 into Sn or un (it should be the same) and common ratio r is just u2/u1.© (i) for the sum to infinity to exit, -1<r<1(ii) simply use the formula for sum to infinity If you've got anymore questions, feel free to ask! Reply Link to post Share on other sites More sharing options...
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