Recursive reference but part not recursive

[rednebmas]

Hey guys, I am trying to capture stuff inside the parentheses. The problem is that it is possible for parentheses to be inside the sqrt.

example string: "sqrt(5^(x+3)-7)"

desired output capture: 5^(x+3)-7

desired output: sqrt{5^(x+3)-7}

The following captures the correct part but it doesn't work if you put sqrt before it.

/\((?:[^()]+|(?R))*\)/

 

For reference: http://php.net/manual/en/regexp.reference.recursive.php

[rednebmas]

sqrt(\((?:[^()]++|(?1))+\))

[rednebmas]

Sorry, I can't figure out how to edit apost...

This: "sqrt(\((?:[^()]++|(?1))+\))" matches "(5^(x+3)-7)" but I need it to match "5^(x+3)-7". How can I remove the outside parentheses?