Just came across a beautiful question.....
If a1, a2, a3, a4 are in HP then
1a1a4\sum_{r=1}^{3}{}ar ar+1 is a root of :
A) x2 + 2x + 15 = 0
B) x2 + 2x - 15 = 0
C) x2 - 2x + 15 = 0
D) x2 - 2x - 15 = 0
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3 Answers
62what is DK? (Dinesh Kartik? the idiot who stopped sachin's 100 and almost prevented gambhir from his 150?)
1061/ar+1 - 1/ar = d
=> ar - ar+1d = arar+1
where d is the CD of the AP
so summing this from r=1 to 3,
we get (a1-a4)/a1a4d
now 1/a4 = 1/a1 + 3d
so the exp is 3
now 3 is a root of (B)
nishant sir pls see ur chatbox
1YUP Asish ... Right.
@Nishant Sir .... DK's not that idiot. DK means Dark Knight.....
though Nishant Bhaiya doesn't watch Eng Movies too often ....lolzzzz Dinesh Kartik HO HO :- D