Explanation:
The root is
-sqr root of 5.
First, we put these roots in the forn of

where a is the root
So we have



To get rid of that square root, let have another root that js the conjugate posive root of 5.


Which will gives us a rational coeffeicent of degree 4.
Why we didn't do

?
Because

If we foiled out we will still have a irrational coeffceint.