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
For i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
Next
9 E: f9 A2 u3 T4 @3 B- EArccos = y
$ L+ g( @3 o1 s5 V7 F; ?# X; t* ]End Function

& Z% P. s( d: }用的是Arccos的微分来算近似值，怎么不对？
( Q3 m& Q& n" ?$ A. b, Z

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
$ o2 ?5 t4 e0 x& E& j5 A& h        Arccos = pi
$ F. f, K6 h2 g+ f' s2 C    Case -1 To 1
        Dim dx As Double, y As Double, i As Long
' ~( J$ ~; {6 Z" y% H        dx = x / n
2 g) _& }' _- G8 x" Y( v0 {  C' v        For i = 1 To n
            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
3 s+ _. m9 I; Q7 J+ H) d2 s        Next
3 ?% F' Y$ b  j2 Z, u' A: R9 Q        Arccos = y + pi / 2
    Case Else
        '异常
1 T+ J" P& f3 m( {/ N, K; L2 \    End Select
, q# W. `+ o- ^, d$ g7 v  n) f& iEnd Function

1 r2 C. d. J* V  [, f搞定了