You multiply numerator and denominator when you want to change a fraction
to be compatible with another fraction, so you can combine them.
You are in fact multiplying by 1,
which does not change a fractions' value, just it's form.
In this case, you can combine the fractions as mentioned, but!
You may also multiply both sides by 2x to simplify
since the sides will still be equal and you no longer have fractions to contend with..