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by Sadowski » Sun Jul 22, 2007 4:26 pm
What is the greatest prime factor of 4^17 - 2^28?

1) 2
2) 3
3) 5
4) 7
5) 11

This doesn't seem that difficult, but after I reduce it to 4^17 - 4^14 or 2^34 - 2^28, I don't see what else I can do. I'm sure I'm missing something quite easy.
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by RM » Sun Jul 22, 2007 10:40 pm
4^17 - 2^28
= (2^2)^17 - 2^28
= 2^34 - 2^28
= 2^28 X (2^6 - 1)
= 2^28 X (64 - 1)
= 2^28 X 63
= 2^28 X 3 X 3 X 7

Prime Factors = 2, 3, 7
Greatest Prime = 7
Answer D
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by Sadowski » Mon Jul 23, 2007 5:59 am
Of course!

Thanks for the help.
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by UmanG » Mon Jul 23, 2007 7:47 am
In fact according to D it's either X=1 or Y=0....

Now if we put only Y=0..equation comes to Z=XZ....

this can't be true since X can hold any value....it means D can't be answer at any cost....
Thanks,
UmanG - restless mind..
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by Sadowski » Mon Jul 23, 2007 7:50 am
This reply is to the wrong post...
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