logo

Ask Questions, Get Answers

 
X
 Search
Want to ask us a question? Click here
Browse Questions
Ad
Home  >>  JEEMAIN and AIPMT  >>  Mathematics  >>  Class11  >>  Sequence and Series
0 votes

Find the sum of the series 1.4 + 2.5 + 3.6----- upto 20 terms.

$\begin{array}{1 1} 2500 \\ 1560 \\ 8270 \\ 3500 \end{array}$

Can you answer this question?
 
 

1 Answer

0 votes
Answer : (d) 3500
$Explanation : \;T_{n}=n(n+3)$
$=n^2+3n$
$S_{n}=\sum\;T_{n}=\sum\;n^2+3\;.\sum\;n$
$=\large\frac{n(n+1)(2n+1)}{6}+3\;.\large\frac{n(n+1)}{2}$
$S_{20}=\large\frac{20*21*41}{6}+3\;.\large\frac{20*21}{2}$
$=2870+630$
$=3500.$
answered Jan 3, 2014 by yamini.v
edited Jan 24, 2014
 

Related questions

Ask Question
student study plans
x
JEE MAIN, CBSE, NEET Mobile and Tablet App
The ultimate mobile app to help you crack your examinations
Get the Android App
...