BETAINV function returns the inverse of cumulative beta distribution. @a is the optional lower bound of @x and @b is the optinal upper bound of @x. If @a is not given, BETAINV uses 0. If @b is not given, BETAINV uses 1.
If @p < 0 or @p > 1 BETAINV returns #NUM! error. If @alpha <= 0 or @beta <= 0, BETAINV returns #NUM! error. If @a >= @b BETAINV returns #NUM! error.
This function is Excel compatible.