How do we rationalize a denominator?
Multiply the whole fraction by the denominator over itself.
If you have a fraction where the denominator (bottom number) is irrational, such as a square root, then multiply the whole fraction by the denominator divided by itself.
Take the example
which has a rational denominator.
Multiply the entire fraction by the denom. divided by itself, like so
More examples are
In this last example I turned