Math Discussion - Why is it impossible to combine

Math- Discussion

Please answer all of the questions below to receive full credit:

1. Why is it impossible to combine the expression (see attached immage)  into a single term? Explain.
2. What does it mean when we say "rationalize the denominator"?
3. Find an example, by finding values for a and b, to show that (see attached immage.
4. Comment on at least one (1) classmate's posting.