小弟正在做一个程序  
就是求这个公式的  给出了d  h    求L
L=(π*(0.25*d*d+h*h)*arccos((d*d-4*h*h)/(d*d-4*h*h))/(180*h)

我写的代码如下
double h,d;
            double π = 3.1415926535897936;
            double a, L, B;
            h = Convert.ToInt32(textBox3.Text);
            d = Convert.ToInt32(textBox4.Text);

            B = ((d * d) - (4 * h * h)) / ((d * d) + (4 * h * h));
            a = Math.Acos(B);
            L = (π * ((0.25 * d * d + h * h) * a) / (180 * h));
            textBox2.Text =Convert.ToString(L);

但是 计算出来的 结果好像 是错误的  希望各位大大指点一二 ~~ 小弟写过了

double h,d;
            double π = 3.1415926535897936;
            double a, L, B;
            h = Convert.ToInt32(textBox3.Text);
            d = Convert.ToInt32(textBox4.Text);

            B = (d * d- 4 * h * h) / (d * d + 4 * h * h);
            a = Math.Acos(B);
            L = (π * ((0.25 * d * d + h * h) * a) )/ (180 * h);
            textBox2.Text =Convert.ToString(L);