Question

Explain what a conjugate is and how you can use it to simplify a radical expression such as (16)/(√11+√7)

Answer 1

it's like in difference of squares
you just take the opposite of the second term
so for (a+b) you have (a-b) as conjugate

It simplifies in the same way as difference of squares does.
If you multiply top and bottom of your expression by the conjugate the effect is to make the radicals go away.