vb中只知道sin(x)的结果，怎么求x

用反三角函数拉
给你定义了一下

'Secant
Public Function Sec(ByVal Number As Double) As Double
Sec = 1 / Cos(Number)
End Function

'Cosecant
Public Function Csc(ByVal Number As Double) As Double
Csc = 1 / Sin(Number)
End Function

'Cotangent
Public Function Ctn(ByVal Number As Double) As Double
Ctn = 1 / Tan(Number)
End Function

'Inverse Sine
Public Function ASin(ByVal Number As Double) As Double
ASin = Atn(Number / Sqr(-Number * Number + 1))
End Function

'Inverse Cosine
Public Function ACos(ByVal Number As Double) As Double
ACos = Atn(-Number / Sqr(-Number * Number + 1)) + 2 * Atn(1)
End Function

'Inverse Secant
Public Function ASec(ByVal Number As Double) As Double
ASec = Atn(Number / Sqr(Number * Number - 1)) + Sgn((Number) - 1) * (2 *
Atn(1))
End Function

'Inverse Cosecan