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Show that a1,a2,...,an,... form an AP wh...

Show that `a_1,a_2,...,a_n,... `form an AP where `a_n`is defined as below : (i) `a_n=3+4n` (ii) `a_n=9-5n`. Also find the sum of the first 15 terms in each case.

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Here, a is the first term, d is the common difference and n is the number of terms and l is the last term.
(i) `a_n = 3 + 4n`
Given,
`nth` term, `a_n = 3 + 4n`
...
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