Quote:
Originally Posted by davieddy
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^5x)/5] + [(x^3x)/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