SOLUTION: evaluate S9 for 1/4, 1, 4, 16...

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Question 1115344: evaluate S9 for 1/4, 1, 4, 16...
Answer by math_helper(2461) About Me  (Show Source):
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+S%5Bn%5D+=+%28a%5B1%5D%2A%281-r%5En%29%29+%2F+%281-r%29+ , +r+%3C%3E+1+
where
+n+ = number of terms
+a%5B1%5D+ = first term
+r+ = common ratio

Here,
+n++=+9+
+a%5B1%5D+=+1%2F4+
and
+r+=+4+


You can plug in the values to find +S%5B9%5D+=+87381%2F4+=+21845.25+