\[\begin{array}{l} {\rm B}\left( {x,y} \right) = \int\limits_0^1 {{t^{x - 1}}{{\left( {1 - t} \right)}^{y - 1}}dt} , \hfill \\ \operatorname{Re} x > 0,{\text{ }}\operatorname{Re} y > 0. \hfill \\ \end{array}\]