SOLUTION: If the sum of the first 10 terms of an arithmetic progression is 4 times the sum of the first 5 terms, find the d in terms of a.
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Question 1108752: If the sum of the first 10 terms of an arithmetic progression is 4 times the sum of the first 5 terms, find the d in terms of a. Answer by ikleyn(52890) (Show Source):
= . <<<---=== Standard formula for the sum of AP
= . <<<---=== Standard formula for the sum of AP
= is equivalent to
= .
=
2a + 9d = 4a + 8d ====> 9d - 8d = 4a - 2a ====> d = 2a.
Answer. d = 2a is the relation between "d" and "a".
