This kind of problem is generally to divide a constant into two numbers as which two numbers, that is, to see if the other one can be pieced together into a complete square.

For example, if this question regards 9 as 2 2+(√ 5) 2, then the root number can be written as a complete square (2-√ 5) 2, and because 2 < √ 5, the root number is √5-2.

Shall I give you another question to practice?

√( 14+6√5) The answer is 3+√5.