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