\[
 - \frac{1}{{\sqrt 3 }}\int {\frac{{\frac{2}{3}dz}}{{\sqrt {\frac{4}{9} - \frac{4}{9}z^2 } }}}  =  - \frac{1}{{\sqrt 3 }}\int {\frac{{\frac{2}{3}dz}}{{\frac{2}{3}\sqrt {1 - z^2 } }}}  =  - \frac{1}{{\sqrt 3 }}\int {\frac{{dz}}{{\sqrt {1 - z^2 } }}}  = ...
\]