Acos function for VB 6?

[Tim8w]

I need an Acos() and Asin() function for VB 6 similar to the built-in Atn() function. Why it was not included in VB, I'll never know.

Thanks,
Tim

 

[CajunCenturion]

Neither function is intrincis to VB, but you can use the following identities to derive these functions:

Arcsin(X) = Atn(X / Sqr(-X * X + 1))

Arccos(X) = Atn(-X / Sqr(-X * X + 1)) + 2 * Atn(1)

Good Luck
--------------
As a circle of light increases so does the circumference of darkness around it. - Albert Einstein

 

[harebrain]

I guess they wanted to see if you'd paid enough attention in math class to
know the identities.

(Based on trig section from Gary Connell's "VB6 from the Ground Up&quot

Public Function Pi() As Double
  Pi = 4 * Atn(1#)
End Function

Public Function ArcSin(ByVal x As Double) As Double
  ArcSin = Atn(x / Sqr(-x * x + 1))
End Function

Public Function ArcCos(ByVal x As Double) As Double
  ArcCos = ArcSin(x) + Pi / 2
End Function

x is in radians. It's left to you to do range-checking for x.

 

[Tim8w]

Thanks for the input guys. I'm still having a problem, however. ArcCos in both your implementations works fine. I have not been able to get a correct value for ArcSin using either impplementation...

Any ideas?

Thanks,
Tim

 

[harebrain]

That's odd: in the functions I supplied ArcCos depends on ArcSin, so if ArcSin doesn't work, how would ArcCos?

Upon further examination, I see that CajunCenturion's ArcCos equation has a leading minus sign in the argument to Atn which I don't: both can't be right.

Ok, who still has their CRC Math Handbook?

Of course, you could always Google for "trig identities"...

 

[Tim8w]

I took your advice. I seached the web for ArcCos and found this code at:

http://www.blibbleblobble.co.uk/Downloads/CodeLibrary/

Public Function ArcCos (x As Variant) As Variant

Select Case x
Case -1
ArcCos = 4 * Atn(1)

Case 0:
ArcCos = 2 * Atn(1)

Case 1:
ArcCos = 0

Case Else:
ArcCos = Atn(-x / Sqr(-x * x + 1)) + 2 * Atn(1)
End Select
End Function

Public Function ArcSin (x As Variant) As Variant

Select Case x
Case -1
ArcSin = 6 * Atn(1)

Case 0:
ArcSin = 0

Case 1:
ArcSin = 2 * Atn(1)

Case Else:
ArcSin = Atn(x / Sqr(-x * x + 1))
End Select
End Function

Seems all I was missing was the extreeme cases.

Thanks all,
Tim