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Old 2007-07-09, 15:52   #7
mfgoode
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Jan 2004
Mumbai,India

80416 Posts
Thumbs up Precise and concise!

Quote:
Originally Posted by davieddy View Post
Thanks FiveMack.
Actually I tried to prove that 3x^4 +5x^2 +7
was divisible by 15. This could indeed be false,
when x is a multiple of 3 and/or 5.
David

And THX Mally - a successful puzzle :)
Look forward to the next!


Hold your horses Davie. Here is a precise and concise solution you can ever get. Thats why I put this problem.

Its the type Alpertron and Maxal will appreciate so here it is.

original Expression = [(x^5-x)/5] + [(x^3-x)/3] + x.
But by Fermat's theorem x^5 - x == 0 mod 5 and x^3 -x ==Mod 3 hence the expression is an integer!

Q.E.D

Mally
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