VB中定义Arccos函数

游侠无极限

我是这样的：
Private Function Arccos(x As Double, n As Long)
Dim i As Long, y As Double
) K! A5 J9 g( A  cFor i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
7 L$ u8 a9 ~' D! YNext
Arccos = y
End Function
" v, E% b+ E! u5 R
用的是Arccos的微分来算近似值，怎么不对？
: G, j: R- t: Z  q

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
        Arccos = 0
    Case -1
1 \9 Q+ W4 N% A7 n        Arccos = pi
: n' h7 t: u5 O: _2 Q    Case -1 To 1
        Dim dx As Double, y As Double, i As Long
        dx = x / n
        For i = 1 To n
- z9 U8 O9 f1 C7 e: o, ~            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
1 R5 N, W+ ?! ]; ]+ u        Next
        Arccos = y + pi / 2
2 k( s* }  F- [' c, O  D3 l) ]    Case Else
        '异常
    End Select
End Function

0 b# U2 a( c$ ~/ b; G% Z搞定了