Question 1192007
<font color=black size=3>
Proof by contradiction:


Assume that 3 is a factor of m. We'll show a contradiction arises from this assumption.
This means m = 3k for some integer k
This further leads to mn = 3k*n = 3(kn)
Showing that mn is a multiple of 3.
But this contradicts the fact that mn is <u>not</u> a multiple of 3. 
Therefore, we must have m be a non-multiple of 3 as well.


Similar steps would apply to show that n must be a non-multiple of 3. This is one application of "without loss of generality" (WLOG) you can do.


Ultimately you should find that we get a contradiction if either m = 3k or n = 3p for integers k and p. Therefore, m and n cannot be multiples of 3.
</font>