Answer :
[tex] \sqrt{81 \: + \: 18 \sqrt{7} \: + \: 7} [/tex]
- Factor the indicated expression:
[tex] \sqrt{(9 \: + \: \sqrt{7} ) ^{2} } [/tex]
- Simplified the index, the root and also the exponent using the number 2.
[tex] \boxed{ \bold{9 \: + \: \sqrt{7} }}[/tex]