A grasshopper has two legs, with one leg it can jump for a, and the other for b, in any direction on the number line. The numbers a and b are real numbers.
What points can a grasshopper hit on a straight line?
A grasshopper has two legs, with one leg it can jump for a, and the other for b, in any direction on the number line. The numbers a and b are real numbers.
What points can a grasshopper hit on a straight line?
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The order of the jumps does not matter: we can jump $a,b,-a,-b$, so we can get any number of the form $\lambda a+\mu b$ for $\lambda,\mu\in\mathbb{Z}$, and no other numbers.
In particular, note that this is a countably infinite number of numbers (infinite because we can choose $\lambda=1,2,3,\dots$ and countable because we can describe each number by a finite description of one set of jumps the grasshopper can take to get there). The real numbers are uncountably infinite, so almost all numbers cannot be reached in this way.