Simplify the expression
\frac{1}{\sqrt{36}} - \sqrt{27} - \frac{1}{\sqrt{27}} - \sqrt{18} + \frac{1}{\sqrt{18}} - \sqrt{9}
1 / [ sqrt 36 - sqrt 27 ] - 1 / [ sqrt 27 - sqrt 18 ] + 1 / [ sqrt 18 - sqrt 9]
1/ [ 6 - sqrt 27 ] - 1 / [ sqrt 27 - sqrt 18] + 1 / [sqrt18 - 3]
[ 6 + sqrt 27 ] / [ 36 - 27] - [ sqrt 27 + sqrt 18] / [ 27 - 18] + [sqrt 18 + 3 ] / [18 - 9]
[ 6 +sqrt 27 ] / 9 - [ sqrt 27 + sqrt 18 ] / 9 + [ sqrt 18 + 3 ] / 9
[ 6 + 3 ] / 9 =
1