纯数学 计算旋转体 体积！

kingchoice00

'圆方程(x-a)^2+(y-b)^2=c^2的定积分(圆弧绕x轴旋转的体积）
' a b  为圆心坐标，e 　f 表示定积分的上下限　我是先显化为　ｘ＝ｆ（ｙ）绕x轴旋转的体积
Public Function dingjf(ByRef a As Double, ByRef b As Double, ByRef c As Double, ByRef e As Double, ByRef f As Double)
Dim pi As Double
pi = 4 * Atn(1)

If a < 0 Then

    dingjf = (f - e) * (pi * (a * a + c * c) - pi * b * b) - (pi / 3#) * ((f - b) * (f - b) * (f - b) - (e - b) * (e - b) * (e - b)) + pi * b * ((f - b) * (f - b) - (e - b) * (e - b)) + 2 * a * pi * (0.5 * (f - b) * Sqr(c * c - (f - b) * (f - b)) + 0.5 * c * c * Arcsin((f - b) / c) - 0.5 * (e - b) * Sqr(c * c - (e - b) * (e - b)) + 0.5 * c * c * Arcsin((e - b) / c))
Else
     dingjf = (f - e) * (pi * (a * a + c * c) - pi * b * b) - (pi / 3#) * ((f - b) * (f - b) * (f - b) - (e - b) * (e - b) * (e - b)) + pi * b * ((f - b) * (f - b) - (e - b) * (e - b)) - 2 * a * pi * (0.5 * (f - b) * Sqr(c * c - (f - b) * (f - b)) + 0.5 * c * c * Arcsin((f - b) / c) - 0.5 * (e - b) * Sqr(c * c - (e - b) * (e - b)) + 0.5 * c * c * Arcsin((e - b) / c))
End If
End Function
'反正炫函数
Public Function Arcsin(ByRef x As Double)
Arcsin = Atn(x / Sqr(-x * x + 1))
End Function

计算结果不对，帮忙分析分析