计算三角形面积

double numberone, double numberTwo, double numberThree//三条边，注意两边之和大于第三编
double doubleS = 0;
            double doubleArea = 0;
            doubleS = (numberone + numberTwo + numberThree) / 2;
            doubleArea = Math.Sqrt(doubleS * (doubleS - numberone)
                         * (doubleS - numberTwo) * (doubleS - numberThree));