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ICSE Class 10 Answered

If the sum of n terms of an AP is 3n^2+2n, find its r^th term.
Asked by Ananya | 20 Feb, 2018, 01:12: PM
answered-by-expert Expert Answer
begin mathsize 16px style Let space straight t subscript 1 equals straight a equals First space term space and space straight t subscript 2 space end subscript equals second space term space of space the space sequence. straight S subscript straight n space equals 3 straight n squared plus 2 straight n straight S subscript 1 space equals space straight a equals 3 cross times 1 plus 2 cross times 1 equals 5 straight S subscript 2 space equals 3 cross times 4 plus 2 cross times 2 straight S subscript 2 equals 16 5 plus straight t subscript 2 equals 16 straight t subscript 2 equals 16 minus 5 straight t subscript 2 equals 11 Hence comma space straight d equals straight t subscript 2 minus straight a straight d equals 11 minus 5 equals 6 straight a equals 5 comma space straight d equals 6 straight t subscript straight r equals straight a plus open parentheses straight r minus 1 close parentheses straight d straight t subscript straight r equals 5 plus open parentheses straight r minus 1 close parentheses cross times 6 straight t subscript straight r equals 5 plus 6 straight r minus 6 straight t subscript straight r equals 6 straight r minus 1 end style
Answered by Sneha shidid | 20 Feb, 2018, 01:50: PM

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ICSE 10 - Maths
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