Consider a sequence whose sum of first n -terms is given by Sₙ = 4n^2 + 6n, n ∈ N , t

English

Gujarati

Hindi

8. Sequences and Series

medium

Consider a sequence whose sum of first $n$ -terms is given by $S_n = 4n^2 + 6n, n \in N$, then $T_{15}$ of this sequence is -

A

$118$

B

$120$

C

$122$

D

$86$

Solution

$T_n = S_n -S_{n-1}$
$\Rightarrow T_n = (4n^2 + 6n) -(4(n -1)^2 + 6(n-1))$
$T_n = 8n + 2 \Rightarrow T_{15} = 122$

Standard 11

Mathematics

Share

Similar Questions

The sides of a triangle are distinct positive integers in an arithmetic progression. If the smallest side is $10$, the number of such triangles is

hard

(KVPY-2012)

$150$ workers were engaged to finish a piece of work in a certain number of days. $4$ workers dropped the second day, $4$ more workers dropped the third day and so on. It takes eight more days to finish the work now. The number of days in which the work was completed is

medium

Find the $25^{th}$ common term of the following $A.P.'s$

$S_1 = 1, 6, 11, …..$

$S_2 = 3, 7, 11, …..$

normal

If ${a^2},\;{b^2},\;{c^2}$ are in $A.P.$, then ${(b + c)^{ – 1}},\;{(c + a)^{ – 1}}$ and ${(a + b)^{ – 1}}$ will be in

hard

The number of terms in the series $101 + 99 + 97 + ….. + 47$ is

easy