# Proofs: Problem 2

### Hints

You aren't allowed to use fractions in your final proof. However, it
may be helpful to write a proof using fractions and then set out
to eliminate them. E.g. can you multiply everything in a sequence
of equations by whatever's in the denominator?

Look at this example to see how to
combine equations without
using fractions.

Suppose I have a=b and c=d. Then I can multiply the first equation
by c to get ac=bc. Multiply the second equation by b to get bc=bd.
Now ac=bc=bd. So ac=bd.

For this kind of proof, it's not always clear what variable to
choose when you multiply both sides by something.
You may have to try several choices.
Two things to watch, to guide what you're doing:

- The two equations need to fit together end-to-end.
So they need to end up the same at one pair of ends.
- The other pair of ends needs to contain xn and ym.