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 Discussion Response Post to:
M
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| Author |
Message |
![[Post New]](/templates/default/images/icon_minipost_new.gif) 14 Apr 2007 20:52:05 IST
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hi i think ans is c
let the common diff. be 'd' nd the 1st term be ' a'
it is given dat t7=15 means a+6d=15............(1)
now t2 * t7* t12 = (a+d)(a+6d)(a+11d)
so now by putting the value of a from (1)
we get f(d)=15*25(9 - d^2)
so by differentiating wrt d we get.........
f'(d)=-2d
now for function to be max. or min. f'(d)=0
so d=0
now f''(d)=-2 this implies dat function is max.
hence c is the ans
hope m correct :)
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this reply: 5 points
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