Math Is Fun Forum

Daniel123

Member

Registered: 2007-05-23

Posts: 663

proof involving base b

Sorry for all the questions! I'm pretty much there on most of them, I just need to iron out a few problems.

My problem here is in part b. I can only show the result if k is even, not if k is odd. Can someone please tell me why? Thanks.

Last edited by Daniel123 (2008-11-02 06:55:52)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: proof involving base b

Maybe I'm misinterpreting, but isn't b) false?

Working in base 10, I think 101 would be an example of the type of number b) is describing.
But 101 isn't divisible by 11, so something's gone wrong.

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Why did the vector cross the road?
It wanted to be normal.

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: proof involving base b

Working in base 10,

101 is not divisible by 11, and k is odd

12021 is divisible by 11, and k is even

1230123 is not divisible by 11, and k is odd

473104731 is divisible by 11, and k is even.

Maybe I'm right then? And the question should specify that k is even? (as I can't see anything wrong with my working)

Last edited by Daniel123 (2008-11-02 07:56:01)

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: proof involving base b

Looks good to me too.

Just for the sake of clarity, it would be a good idea to write out f(x) before computing f(b).

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: proof involving base b

Great, thanks