The sum of first 7 terms of an A.P. is 49 and that of first 17 terms of it is 289. Find the sum of first n terms.
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The sum of first 7 terms of an A.P. is 49 and that of first 17 terms of it is 289. Find the sum of first n terms.

KnowledgeBoat · Accepted Answer

Let the first term of A.P. be a and common difference = d. Given, sum of first 7 terms of an A.P. is 49, Given, sum of first 17 terms of an A.P. is 289, Subtracting (i) from (ii) we get, ⇒ a + 8d - (a + 3d) = 17 - 7 ⇒ a - a + 8d - 3d = 10 ⇒ 5d = 10 ⇒ d = 2. Substituting value of d in (i) we get, ⇒ a + 3(2) = 7 ⇒ a + 6 = 7 ⇒ a = 1. Hence, sum of n terms = n².

Mathematics

The sum of first 7 terms of an A.P. is 49 and that of first 17 terms of it is 289. Find the sum of first n terms.

AP

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Mathematics

The sum of first 7 terms of an A.P. is 49 and that of first 17 terms of it is 289. Find the sum of first n terms.

AP

Related Questions

Find the sum of first 12 natural numbers each of which is a multiple of 7.

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