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Algebra

Scorching goIITian

 Joined: 9 Jun 2008 Post: 223
30 Jun 2009 22:31:29 IST
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6
325
find the nth term
Engineering Entrance , JEE Main , JEE Advanced , Mathematics , Algebra

find the nth term of the series 2.2+4.22+7.23+11.23+16.2^5................................

Hot goIITian

Joined: 20 Jun 2008
Posts: 191
30 Jun 2009 22:40:26 IST
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(2^n)(n^2+n+2)/2

Scorching goIITian

Joined: 9 Jun 2008
Posts: 223
30 Jun 2009 22:41:13 IST
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hey i donno the ans can u give me the soln.

Scorching goIITian

Joined: 9 Jun 2008
Posts: 223
30 Jun 2009 22:43:57 IST
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harini do me a favor.And i will rate u if u have given me the ans.

Hot goIITian

Joined: 20 Jun 2008
Posts: 191
30 Jun 2009 22:48:18 IST
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ok fine bro,

2^n factor in the ans is obvious.

just look at the other part.

2,4,7,11,16................

or

2

2+2

2+2+3

2+2+3+4     etc

2+3+4... can be added up by the summation formula if we add and subtract 1

so{ 2+[(n^2+n-2)/2]}2^n

upon simplification u get the ans

Scorching goIITian

Joined: 9 Jun 2008
Posts: 223
30 Jun 2009 22:52:28 IST
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have u check it for 4.its not working am i rite.

Hot goIITian

Joined: 20 Jun 2008
Posts: 191
30 Jun 2009 22:55:45 IST
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if the 4 th term is not with 2^4 it doesn't seem to be a sequence..................

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