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Ask iit jee aieee pet cbse icse state board community Community Discussion Question: IIT 2007 Q!!!!!!!!!
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varshavallig (798)

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

Varsha
be cool,
tomorrow is what we make it today,
so if u can dream it , u can make it .
life is an ice cream ,eat it before it melts away!!!!!!!!!
varsha

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Avinash_Bhat (576)

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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) )
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cuteprincess (17)

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hey what is Q there????!!!
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varshavallig (798)

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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.
!!!!!!!!!!!!!!!!!!!!!!!

Varsha
be cool,
tomorrow is what we make it today,
so if u can dream it , u can make it .
life is an ice cream ,eat it before it melts away!!!!!!!!!
varsha

SmileyCentral.com




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priyesh (1584)

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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
 
 

"Imagination is more important than knowledge."
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sugeet (36)

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r2 + r/2(r-1)(2r-1)
got it by sum of r terms formulae
hope not wrong

>>sugeet->


--catalysingsuccess
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varshavallig (798)

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

Varsha
be cool,
tomorrow is what we make it today,
so if u can dream it , u can make it .
life is an ice cream ,eat it before it melts away!!!!!!!!!
varsha

SmileyCentral.com




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sunip_the_mini_mastermind (133)

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u wrote out the wrong question ...the question is to find[ ][ ] Vr
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aritra (0)

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its all very simple, folks
the r2 term will be r3
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varshavallig (798)

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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.
!!!!!!!!

Varsha
be cool,
tomorrow is what we make it today,
so if u can dream it , u can make it .
life is an ice cream ,eat it before it melts away!!!!!!!!!
varsha

SmileyCentral.com




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priyesh (1584)

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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)]

"Imagination is more important than knowledge."
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priyesh (1584)

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@sugeet ur signature width is very large please reduce it

"Imagination is more important than knowledge."
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