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Fifth term of an A.P is 13 and sum of its first 15 terms is 285. Find 14th termof this A.P and also sum of its first n terms. |
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Answer» nth term = a + (n-1)d where a = first term and d = difference 5th term = 13 a + 4d = 13 Sn = n/2 (2a + (n-1)d) S15 = 285 = 15/2 (2a + 14d) 19 = 2/2 (a + 7d) a + 7d = 19 a + 7d - a - 4d = 19 - 13 3d = 6 d = 2 a + 8 = 13 a = 5 14th term = a + 13d = 5 + 13*2 = 5 + 26 = 31 Sn = n/2(2*5 + (n-1)2) = n(5+n-1) = n(4+n) If you find this answer helpful then like it. |
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