F 3 ( Π , Ξ ) = 2 P 3 ( Π , Ξ ) R 3 ( Π , Ξ ) P 3 ( Π , Ξ ) + R 3 ( Π , Ξ ) , {\displaystyle F_{3}(\Pi ,\Xi )={\frac {2P_{3}(\Pi ,\Xi )R_{3}(\Pi ,\Xi )}{P_{3}(\Pi ,\Xi )+R_{3}(\Pi ,\Xi )}},}
