Point::distance PHP Method

    static function distance($point1, $point2)
    {
        //if( !isset( self::$distanceTable[ $point1->guid ][ $point2->guid ] ) ) {
        $a = $point2->x - $point1->x;
        $b = $point2->y - $point1->y;
        $distance = round(sqrt(pow($a, 2) + pow($b, 2)), 1);
        self::$distanceTable[$point1->guid][$point2->guid] = $distance;
        self::$distanceTable[$point2->guid][$point1->guid] = $distance;
        //}
        return self::$distanceTable[$point1->guid][$point2->guid];
    }

 static function aireTriangle($pointA, $pointB, $pointC)
 {
     $AB = Point::distance($pointA, $pointB);
     $BC = Point::distance($pointB, $pointC);
     $AC = Point::distance($pointC, $pointA);
     return sqrt(($AB + $BC + $AC) * (-$AB + $BC + $AC) * ($AB - $BC + $AC) * ($AB + $BC - $AC)) / 4;
 }