VB中定义Arccos函数

游侠无极限

我是这样的：
0 \) V* `; e5 W" [' T. }Private Function Arccos(x As Double, n As Long)
) q7 S# v  V+ z$ M1 C" s3 fDim i As Long, y As Double
6 w( l$ Y/ m4 v" E9 w3 kFor i = 1 To n
    y = y + (-1 / Sqr(1 + (x / n * i) ^ 2)) * x / n
Next
Arccos = y
End Function
: ]  A: J9 u: U4 g9 A# I
9 B0 q1 L# X  W- m* y/ |% W用的是Arccos的微分来算近似值，怎么不对？
0 U8 s& i5 R" @! T' U3 a

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
3 X. i) M: c# @  x" T7 O    Select Case x
8 R% I4 u$ A8 e& x8 T7 L' A2 i- R    Case 1
        Arccos = 0
    Case -1
1 U/ v7 r5 u5 ?1 i7 p) A$ p7 h7 [        Arccos = pi
+ i; ?  `4 g6 J6 r. I2 `* d3 O    Case -1 To 1
        Dim dx As Double, y As Double, i As Long
        dx = x / n
7 {( d$ ]" X, H' O        For i = 1 To n
1 V- J/ {- f8 r) ^$ I/ }; K            y = y + (-1 / Sqr(1 - (dx * i + dx / 2) ^ 2)) * dx
' D, e. [3 w9 P5 M# N/ j1 u        Next
5 w4 }/ j' @) e- {        Arccos = y + pi / 2
, ~- x7 ~0 l8 B- u1 Q    Case Else
        '异常
    End Select
) A8 P8 w6 l. ]$ F- d3 z- DEnd Function

. V% `0 \% j) o% D- d- z搞定了