VB中定义Arccos函数

游侠无极限

我是这样的：
! c. N) n( g( [Private Function Arccos(x As Double, n As Long)
3 A( p' L: _( IDim i As Long, y As Double
For i = 1 To n
, V& H3 S2 z2 w# o6 _    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
Next
Arccos = y
End Function
3 h+ ~9 o$ ]1 _; u
0 p7 Z/ A9 r0 y0 X# L) I% d用的是Arccos的微分来算近似值，怎么不对？
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煎饼

公式对就没有问题拉

游侠无极限

Const pi As Double = 3.14159265359
Private Function Arccos(x As Double, n As Long) ' n 为函数精度，建议为100
    Select Case x
    Case 1
/ q8 z9 J& q  x0 a4 ~9 l        Arccos = 0
    Case -1
; i/ v8 R- f3 M: i! X' B        Arccos = pi
( o  p$ \7 L6 y6 h! z9 y    Case -1 To 1
- C, z2 Q( m4 q  B0 m/ T$ f        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
' v2 _  n5 B; P* Q8 r, Y" \6 u; n        Next
1 g  G. M: n. G! Z+ B: X# f        Arccos = y + pi / 2
    Case Else
        '异常
6 H' d4 x1 q5 e4 ]& G    End Select
5 N2 [  Y2 r+ iEnd Function
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8 W3 R. Q1 r8 N8 U搞定了