SOLUTION: the sum of the first 6 terms of the geometric sequence 1, -2, 4, -8, ... is ?
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Question 472812: the sum of the first 6 terms of the geometric sequence 1, -2, 4, -8, ... is ?
Answer by htmentor(1343) (Show Source): You can put this solution on YOUR website!
The common ratio is -2/1 = -2
The sum of the first n terms of a geometric sequence is:
where a is the 1st term of the sequence
Putting in n = 6, a = 1 and r = -2, we get:
Sum = ->
This gives Sum = -21
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