Home » Ask & Discuss » Mathematics. » Algebra « Back to Discussion



Algebra

varsha valli g.'s Avatar
Blazing goIITian

Joined: 31 Jan 2007
Post: 515
9 Apr 2008 21:06:31 IST
0 People liked this
11
794 View Post
IIT 2007 Q!!!!!!!!!
None

Let r V denote the sum of the first r terms of an arithmetic progression (A.P.) whose first term is r and the
common difference is (2r-1) .
Let  Tr= Vr+1 -Vr -2 andQr= Tr+1- Tr  for r = 1, 2,?.
 
find Vr!!!!!!!!!!!!!!!!!!
plz reply soon
rates assured
!!!!!!!!!!!!!!!!!!


Share this article on:

Comments (11)

Avinash Bhat's Avatar

Blazing goIITian

Joined: 2 Apr 2007
Posts: 360
9 Apr 2008 22:06:10 IST
1 people liked this

YOUR QUESTION IS JUST TO FIND Vr

First term  =  r

Common Difference  =  ( 2r - 1 )

Sum of first r terms  =  Vr 

                              =  ( r / 2 )( 2r  +  (r - 1)(2r - 1) )
F K's Avatar

Cool goIITian

Joined: 9 Apr 2008
Posts: 44
10 Apr 2008 08:45:40 IST
0 people liked this

hey what is Q there????!!!
varsha valli g.'s Avatar

Blazing goIITian

Joined: 31 Jan 2007
Posts: 515
10 Apr 2008 08:49:33 IST
0 people liked this

but thats not the right ans .
me too did the same way.in this method v get a cube term.but in the solution there is no such term.

the ans is Vr= r^2-r^2/2 +r/2
hows that possible.
!!!!!!!!!!!!!!!!!!!!!!!
Priyesh's Avatar

Blazing goIITian

Joined: 18 Feb 2007
Posts: 1042
10 Apr 2008 09:53:22 IST
1 people liked this

@varshavallig
then ans given in your book is wrong!!!!!!!!!!!!!
 
because
 
putting r = 2 in ur ans sum comes out as 3
 
but sum of first two terms is 2 + 5 = 7
 
 
sugeet's Avatar

Cool goIITian

Joined: 3 Apr 2008
Posts: 79
10 Apr 2008 13:50:11 IST
1 people liked this

r2 + r/2(r-1)(2r-1)
got it by sum of r terms formulae
hope not wrong
varsha valli g.'s Avatar

Blazing goIITian

Joined: 31 Jan 2007
Posts: 515
10 Apr 2008 15:03:28 IST
0 people liked this

it was given here: http://www.careerlauncher.com/common/analyses/2007_IITJEE_paper1.pdf
plz have a look.
!!!!!!!!!!!!!!!!!!
sunip dutta's Avatar

Scorching goIITian

Joined: 24 Aug 2007
Posts: 211
10 Apr 2008 15:08:10 IST
0 people liked this

u wrote out the wrong question ...the question is to find[ ][ ] Vr

New kid on the Block

Joined: 29 Feb 2008
Posts: 19
10 Apr 2008 15:15:15 IST
0 people liked this

its all very simple, folks
the r2 term will be r3
varsha valli g.'s Avatar

Blazing goIITian

Joined: 31 Jan 2007
Posts: 515
10 Apr 2008 15:21:33 IST
0 people liked this

@ sunip_the_mini_mastermind
but there in the step for finding Vr ,it is diff from what v got ,so if the 1st step is wrong,obviously sum of Vr is also wrong.
!!!!!!!!
Priyesh's Avatar

Blazing goIITian

Joined: 18 Feb 2007
Posts: 1042
10 Apr 2008 15:34:51 IST
0 people liked this

Vr = r/2(2r + (r-1)(2r-1)] = 1/2[2r^3 - r^2 + r)
 
 
Vr = 1/2[ 2r^3 - r^2 + r]
 
= 1/2[2(n(n+1)/2)^2 - n(n+1)(2n+1)/6   + n(n+1)/2 
 
= 1/12[n(n+1)(3n^2 + n + 2)]
Priyesh's Avatar

Blazing goIITian

Joined: 18 Feb 2007
Posts: 1042
10 Apr 2008 15:36:57 IST
0 people liked this

@sugeet ur signature width is very large please reduce it



Quick Reply


Reply

Some HTML allowed.
Keep your comments above the belt or risk having them deleted.
Signup for a avatar to have your pictures show up by your comment
If Members see a thread that violates the Posting Rules, bring it to the attention of the Moderator Team
Free Sign Up!

Preparing for IIT-JEE ?

Arihant Revision Package for IIT JEE - Books, Practice Tests + Rank Predictor


@ INR 1,995/-

For Quick Info

Name

Mobile No.

Find Posts by Topics

Physics.

Topics

Mathematics.

Chemistry.

Biology

Parents

Board

Fun Zone

Sponsored Ads