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algebra intermediate

Problem

If the second term of a geometric sequence of real numbers is and the fifth term is then what is the fourteenth term?
Solution


Let the first term be and the common ratio be Because the second term is we have Because the fifth term is we have Dividing this by we have Therefore, So, Therefore, the fourteenth term is



To get from the second term to the fifth term, we multiply by the common ratio, three times. Therefore, multiplying by gives us So, Rather than finding we note that to get to the fourteenth term from the fifth term, we multiply by nine times, which is the same as multiplying by three times. So, the fourteenth term is
Final answer
-8192