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![[Post New]](/templates/default/images/icon_minipost_new.gif) 22 Apr 2008 23:22:49 IST
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If a1,a2,a3........an are in HP,then find the value of the expression a1a2+a2a3.....+an-1an a)(n-1) a1an b)n(a1 - an) c)(n-1)(a1-an) d)na1an
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"Many of the things you can count,dont count....
Many of the things you cant count,really do count...."-Albert Einstein
"The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them"-William Bragg
"An inexplicable fact is infinitely preferable to an incomprehensible mystery"-F. Soddy
RISHIPRATIM MAZUMDAR
NIT DURGAPUR
1ST YEAR,ELECTRONICS AND COMMUNICATIONS
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22 Apr 2008 23:53:39 IST
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any1????
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"Many of the things you can count,dont count....
Many of the things you cant count,really do count...."-Albert Einstein
"The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them"-William Bragg
"An inexplicable fact is infinitely preferable to an incomprehensible mystery"-F. Soddy
RISHIPRATIM MAZUMDAR
NIT DURGAPUR
1ST YEAR,ELECTRONICS AND COMMUNICATIONS
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22 Apr 2008 23:56:34 IST
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Answer is d na1 an
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23 Apr 2008 00:07:03 IST
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can be done by hit and trial
take the numbers in HP = 1/2 , 1/4 , 1/6
here n = 3
now put values in the four options
answer is a
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23 Apr 2008 00:12:01 IST
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@harshthakar...
hw can u say dat its d...
if n=2,then we get a1a2=2a1a2
dats nt possibl...
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"Many of the things you can count,dont count....
Many of the things you cant count,really do count...."-Albert Einstein
"The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them"-William Bragg
"An inexplicable fact is infinitely preferable to an incomprehensible mystery"-F. Soddy
RISHIPRATIM MAZUMDAR
NIT DURGAPUR
1ST YEAR,ELECTRONICS AND COMMUNICATIONS
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23 Apr 2008 00:24:44 IST
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the ans is a.
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23 Apr 2008 00:29:59 IST
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c a1,a2,a3...r in hp means 1/a1,1/a2...r in ap so 2/a2=1/a1+1/a3 so solvin u get a2a3+a3a4=2a1a3 similar ly u can try 4 othres so itz a) (n-1)a1a3
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23 Apr 2008 00:34:15 IST
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yes even i'm getting the ans a
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23 Apr 2008 00:51:15 IST
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.1/a1,1/a2,.....1/an are in ap let d be the common difference 1/a2 - 1/a1=d => (a1-a2)/d = a1.a2 similarly (a2-a3)/d = a2.a3 ...... (an-2 - an-1)/d = an-2.an-1. (an-1 - an)/d = an-1.an. now by adding ew get a1.a2 + a2.a3 +.....an-2.an-1.+an-1.an. = (a1-an)1/d we know that 1/an - 1/a1 = (n-1)d => (a1-an) = (n-1)da1.an . so a1.a2 + a2.a3 +.....an-2.an-1.+an-1.an. = (n-1)a1.an .
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23 Apr 2008 11:40:09 IST
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a1a2=(a1-a2)/d d= common diff off HP
so {(a1-a2) +(a2-a3)+.....+ (an-1 - an)}/d=(a1-an)/d
now 1/an-1/a1=(n-1)d=(a1-an)/(a1an)
so substituting: we get answer= (n-1)a1an
hence a)
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25 Apr 2008 00:01:58 IST
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thanx,evry1!!!!
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"Many of the things you can count,dont count....
Many of the things you cant count,really do count...."-Albert Einstein
"The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them"-William Bragg
"An inexplicable fact is infinitely preferable to an incomprehensible mystery"-F. Soddy
RISHIPRATIM MAZUMDAR
NIT DURGAPUR
1ST YEAR,ELECTRONICS AND COMMUNICATIONS
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