The WEIBULL function returns the Weibull distribution. If the @cumulative boolean is true it will return: 1 - exp (-(@x/@beta)^@alpha), otherwise it will return (@alpha/@beta^@alpha) * @x^(@alpha-1) * exp(-(@x/@beta^@alpha)).
If @x < 0 WEIBULL returns #NUM! error. If @alpha <= 0 or @beta <= 0 WEIBULL returns #NUM! error.