public static function PDF($x, $a, $b) { Support::checkLimits(self::LIMITS, ['x' => $x, 'a' => $a, 'b' => $b]); if ($x < $b) { return 0; } $abᵃ = $a * $b ** $a; $xᵃ⁺¹ = pow($x, $a + 1); return $abᵃ / $xᵃ⁺¹; }