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If the sum of n terms of a series is2n^...

If the sum of n terms of a series is`2n^(2)+5n` for all values of n, find its 7th term.

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Given, `S_(n)=2n^(2)+5n`
`implies S_(n-1)=2(n-1)^(2)+5(n-1)=2n^(2)+n-3`
`therefore" "T_(n)=S_(n)-S_(n-1)=(2n^(2)+5n)-(2n^(2)+n-3)=4n+3`
Hence, `T_(7)=4xx7+3=31`
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ARIHANT MATHS-SEQUENCES AND SERIES-Exercise (Questions Asked In Previous 13 Years Exam)
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  11. Let A1 , G1, H1denote the arithmetic, geometric and harmonic means re...

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