VB中定义Arccos函数

游侠无极限

我是这样的：
9 n9 ?" ]! ?1 W1 l- B4 k6 X7 WPrivate Function Arccos(x As Double, n As Long)
% I1 C, f; T* D4 D( ?; e+ H7 UDim i As Long, y As Double
For i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
Next
# Z* L4 ^' k0 [, |4 ?Arccos = y
! q; e% P! a$ i2 c; CEnd Function
: ~( x7 S9 I# |# D- |, D
用的是Arccos的微分来算近似值，怎么不对？
0 X! R! @- d% c/ b

煎饼

公式对就没有问题拉

游侠无极限

Const pi As Double = 3.14159265359
0 O& I& {9 c, r8 T5 e5 bPrivate Function Arccos(x As Double, n As Long) ' n 为函数精度，建议为100
    Select Case x
    Case 1
  u% [3 e% g) Q- Q. u+ s        Arccos = 0
! h5 I" q1 L) ]! w    Case -1
- v7 @( q) N' |: P# t$ i: I        Arccos = pi
    Case -1 To 1
6 W$ H: Y) J( F+ F' K        Dim dx As Double, y As Double, i As Long
        dx = x / n
        For i = 1 To n
            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
; F5 c4 Z, m, n) d9 r) F        Next
/ ?+ l  H7 S+ u9 K6 I4 J" U        Arccos = y + pi / 2
( F- c! ~6 o; ]. D    Case Else
  n1 ~$ A6 [: t        '异常
    End Select
End Function

搞定了