To simplify the radical, factorize the number under it using the prime number
Since 252 is an even number, then let us divide it by the 1st prime number 2
[tex]\frac{252}{2}=126[/tex]since 126 is an even number, then divide it by 2 again
[tex]\frac{126}{2}=63[/tex]Now 63 is an odd number and sum of its digit = 6 + 3 = 9, then
Divide it by the 2nd prime number 3
[tex]\frac{63}{3}=21[/tex]Since 21 is divisible by 3, divide it by 3 again
[tex]\frac{21}{3}=7[/tex]Then 252 = 2 x 2 x 3 x 3 x 7, put them under the radical
[tex]\sqrt[]{252}=\sqrt[]{2\times2\times3\times3\times7}[/tex]Each number repeated twice can go out the radical, then
2 and 3 will go out the radical
[tex]\begin{gathered} \sqrt[]{252}=2\times3\times\sqrt[]{7} \\ \sqrt[]{252}=6\sqrt[]{7} \end{gathered}[/tex]The simplest form of the radical is 6 square root 7
[tex]\begin{gathered} \sqrt[]{252}=\sqrt[]{4}\times\sqrt[]{63} \\ =2\times\sqrt[]{63} \\ =2\times\sqrt[]{9}\times\sqrt[]{7} \\ =2\times3\times\sqrt[]{7} \\ =6\times\sqrt[]{7} \\ =6\sqrt[]{7} \end{gathered}[/tex]