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Algebra

Blazing goIITian

Joined:	31 Jan 2007
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9 Apr 2008 21:06:31 IST

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794

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= V_r+1 -V_r -2 andQ_r= T_r+1- T_r for r = 1, 2,?.

find V_r!!!!!!!!!!!!!!!!!!

plz reply soon

rates assured

!!!!!!!!!!!!!!!!!!

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Comments (11)

Avinash Bhat

Blazing goIITian

Joined: 2 Apr 2007

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9 Apr 2008 22:06:10 IST

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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

Cool goIITian

Joined: 9 Apr 2008

Posts: 44

10 Apr 2008 08:45:40 IST

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hey what is Q there????!!!

varsha valli g.

Blazing goIITian

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Posts: 515

10 Apr 2008 08:49:33 IST

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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

Blazing goIITian

Joined: 18 Feb 2007

Posts: 1042

10 Apr 2008 09:53:22 IST

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@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

Cool goIITian

Joined: 3 Apr 2008

Posts: 79

10 Apr 2008 13:50:11 IST

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r² + r/2(r-1)(2r-1)

got it by sum of r terms formulae

hope not wrong

varsha valli g.

Blazing goIITian

Joined: 31 Jan 2007

Posts: 515

10 Apr 2008 15:03:28 IST

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

sunip dutta

Scorching goIITian

Joined: 24 Aug 2007

Posts: 211

10 Apr 2008 15:08:10 IST

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u wrote out the wrong question ...the question is to find_{[ ]}

^{[ ]} V_r

aritra

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10 Apr 2008 15:15:15 IST

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its all very simple, folks

the r

2 term will be r3

varsha valli g.

Blazing goIITian

Joined: 31 Jan 2007

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10 Apr 2008 15:21:33 IST

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@ 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

Blazing goIITian

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10 Apr 2008 15:34:51 IST

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Vr = r/2(2r + (r-1)(2r-1)] = 1/2[2r^3 - r^2 + r)

Vr = 1/2[ 2

r^3 -

r^2 +

= 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

Blazing goIITian

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Posts: 1042

10 Apr 2008 15:36:57 IST

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@sugeet ur signature width is very large please reduce it

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