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