VB中定义Arccos函数

游侠无极限

我是这样的：
) v  Z0 X% l3 G" l1 d: mPrivate Function Arccos(x As Double, n As Long)
Dim i As Long, y As Double
* F& w/ F% H" j5 D) l( O/ ?3 l* RFor i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
. G7 g; c% f" w7 c( J# HNext
Arccos = y
( F8 N0 B7 f9 `End Function

用的是Arccos的微分来算近似值，怎么不对？

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
1 h9 _# @. z: [0 i  t9 P    Select Case x
! v# `9 S% J7 @& F* c, g    Case 1
" Z" X2 \5 b6 D) R7 [& v        Arccos = 0
    Case -1
        Arccos = pi
    Case -1 To 1
        Dim dx As Double, y As Double, i As Long
        dx = x / n
        For i = 1 To n
' K% K- G1 F5 \& Z$ m# D            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
        Next
        Arccos = y + pi / 2
    Case Else
" \, R/ Z, h4 h. m. }9 k; s  h0 L        '异常
    End Select
  V* X, Q3 g) @% P$ fEnd Function

6 z5 H4 w3 }5 e搞定了