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
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](https://images.topperlearning.com/topper/tinymce/cache/2323bcc042d594ce7d6eeb43af81343e.png)
Hence, the 8th term is 71.
Answered by Renu Varma | 22 Sep, 2020, 12:47: PM
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