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Question

Find the sum of first $15$ terms of the sequence whose $n^{t h}$ term is $3 + 4 n$ .
$525$
$425$
$495$
$N o n e o f t h e s$

A

N o n e o f t h e s

B

525

C

425

D

495

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Solution

Verified by Toppr

$n^{t h}$ term = 3+4 n
$1^{s t}$ term = 3+4(1)=7
$2^{n d}$ term = 3+4(2)=11
$3^{r d}$ term 3+4(3)=15
It is an AP with a=7, d=4
$S_{15} = \frac{15}{2} [2 (7) + 14 (4)]$
$= 15 [7 + 28]$
$= 525$

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