Thursday, June 12, 2008

Is No One Rational?

I ran into a math subproblem in the course of a bigger problem. I thought I'd give the Internet a shot before posting the answer. Here it is:

Show that for any finite set of positive real numbers, there must exist some number x such that x times each of the numbers in the set produces an irrational number.

Or rephrased:

If n runners start out together on an infinite race, each at a constant speed, which is different from the others' speeds, show that at some time each one will be an irrational distance from the start line.

Just a reminder: irrational numbers are those that cannot be written as a fraction a/b with a and b both whole numbers.

3 comments:

Natalie Larson said...

Interesting problem!

Could you take sqrt.(x-(sqrt.(x))+pi) ?

Not the most simple or elegant:)

wellons said...

Natalie,

That function is very interesting, because for any rational input x, the result of the function is irrational. However, the function is too sophisticated! This question is asking only about a function of the form f(x) = bx, where "b" is some constant.

Jonathan

Natalie Larson said...
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