Problem
In an arithmetic sequence of positive numbers, the common difference is twice the first term, and the sum of the first six terms is equal to the square of the first term. Find the first term of the sequence.
Solution
36.
If a is the first term, then 2a is the common difference between successive terms, so the sum of the first six terms is
a + (a + 2a) + (a + 4a) + (a + 6a) + (a + 8a) + (a + 10a) = 36a
which also equals a2, so a = 36 is the first term.
2006-09-07
01:53:25
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2 answers
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Anonymous
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Education & Reference
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