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[Post New]2 Mar 2008 20:28:09 IST
    Subject: Re:if a,b,c,d are in H.P, prove that ab + bc +cd=3ad
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sboosy (3063)

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Olaaa!! Perrrfect answer. 539  [723 rates]
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a , b , c , d are in HP
1/a 1/b 1/c 1/d  in AP
1/b - 1/a = 1/c-1/b = 1/d-1/c = k
a-b = kab
b-c = kbc
c-d = kcd
a-d = k(ab+bc+cd)
 
1/d - 1/a = 3k
so a-d = 3kad
so
ab+bc+cd = 3ad
 
 this reply: 12 points  (with 2 Olaaa!! Perrrfect answer.   in 3 votes )   [?]
 
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