k = 1 ∑ ∞ k ( − 1 ) k + 1 H k = 2 1 ( ζ ( P ) − lo g 2 ( Q ) )
If the above equation is satisfied by positive integers P and Q . Find P Q .
H n is the n t h harmonic number.
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Yeah first time your good problem took me less than 10 mins to solve. Even I did it in the same method, except for a few more steps. Your questions have strengthened me man. Thanks a lot! Do try my problem once. This one is inspired by u.
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Thanks,and congratulations!
hahahah gud one aditya :)
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@Aman Raimann your hot integrals r damn amazing. My next aim is to learn about the functions you've used and to solve your problem.
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@Aditya Kumar – haahaha ..thnxx dude.. try them !! i think they are much harder only 2 questions are easy ... :)
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@Aman Rajput – Currently u r in which college??
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@Aditya Kumar – jamia millia islamia... see my profile
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@Aman Rajput – I'm sorry but I haven't heard of this college. U didn't get into IIT??
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@Aditya Kumar – this is central govt university at delhi.. . i didnt get iit college because i am weak in chemistry :P
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@Aman Rajput – This is the same problem I'm facing. Maths and physics r easy but chem :'(
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@Aditya Kumar – yaa right /// that tym i was just a zero in chemistry ...
well tomorrow is my interview in college so . gudnyt ... and hey my actual name is Aman Rajput.
i already mailed brilliant@support... in order to change my profile name... but got no response .. :'( so gudnyt buddyy .... we'll talk later... in another solved problem :D
@Aditya Kumar – you should study different functions.. in order to solve more problems by simpler methods .
for e.g. 0 ∫ π / 2 lo g ( \sinx ) d x .this solved question in many textbooks of india with the famous procedure which u know very well... but if you know the polygamma you can solve it in 2 lines... instead of using 15 lines as in NCERT books..
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@Aman Rajput – How much time would it take me to learn Polygamma function
( link try to do this problem please
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Using integral representation n = 1 ∑ ∞ n ( − 1 ) n + 1 H n = − ∫ 0 1 n = 1 ∑ ∞ ( − x ) n H n x d x
Now:
− n = 1 ∑ ∞ ( − x ) n H n = − n = 1 ∑ ∞ x n k = 0 ∑ n − 1 ( − 1 ) k n − k ( − 1 ) n − k = − n = 0 ∑ ∞ ( − x ) n ⋅ k = 1 ∑ ∞ k ( − x ) k = 1 + x lo g ( 1 + x )
Thus
I = ∫ 0 1 1 + x lo g ( 1 + x ) x d x = ( − 2 1 lo g 2 ( 1 + x ) − Li 2 ( − x ) ) ∣ ∣ ∣ ∣ x = 0 x = 1 = − 2 1 lo g 2 ( 2 ) − Li 2 ( − 1 )
But Li 2 ( − 1 ) = ∑ k = 1 ∞ k 2 ( − 1 ) k = ( 2 1 − 2 − 1 ) ζ ( 2 ) = − 2 1 ζ ( 2 ) .Thus
I = 2 1 ( ζ ( 2 ) − lo g 2 ( 2 ) )