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ICSE Class 10 Answered

The sum of n natural number is 5n2 - 4n, find its 8th term
Asked by ruchitripathi96167 | 22 Sep, 2020, 12:16: PM
answered-by-expert Expert Answer
Given: Sn = 5n2 - 4n
straight t subscript 8 equals straight S subscript 8 minus straight S subscript 7 equals open parentheses 5 cross times 8 squared minus 4 cross times 8 close parentheses minus open parentheses 5 cross times 7 squared minus 4 cross times 7 close parentheses equals 5 cross times open parentheses 8 squared minus 7 squared close parentheses minus 4 cross times open parentheses 8 minus 7 close parentheses equals 5 cross times 15 minus 4 equals 75 minus 4 equals 71
Hence, the 8th term is 71.
Answered by Renu Varma | 22 Sep, 2020, 12:47: PM

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