Q:

How to make a pendulum swing along a circles circumference

I am attempting to make a pendulum that will have user inputted string length. I am stuck on the issue of how to keep a "constant" string length, the issue is, as the string gets put at an angle the string stays at the same length but due to it being at an angle it shortens, I have tried to remedy this with this code:

If Angle > 0 Then
        If Angle < 50 Then
            x = Asin(Angle) * (LengthOfString + (Angle * 70))
            y = Acos(Angle) * (LengthOfString + (Angle * 70))
            e.Graphics.DrawLine(Pens.Black, 270, 0, (270 + x), (0 + y))
        Else
            x = Asin(Angle) * (LengthOfString + ((100 - Angle) * 70))
            y = Acos(Angle) * (LengthOfString + ((100 - Angle) * 70))
            e.Graphics.DrawLine(Pens.Black, 270, 0, (270 + x), (0 + y))
        End If
    Else
        Angle = Angle ^ 2
        Angle = Sqrt(Angle)
        If Angle < 50 Then
            x = Asin(Angle) * (LengthOfString + (Angle * 70))
            y = Acos(Angle) * (LengthOfString + (Angle * 70))
            e.Graphics.DrawLine(Pens.Black, 270, 0, (270 - x), (0 + y))
        Else
            x = Asin(Angle) * (LengthOfString + ((100 - Angle) * 70))
            y = Acos(Angle) * (LengthOfString + ((100 - Angle) * 70))
            e.Graphics.DrawLine(Pens.Black, 270, 0, (270 - x), (0 + y))
        End If
        End If

Using the (Angle * 70) was a complete fluke, I first attempted to just do LengthOfString + Angle hoping that the length of that would fix it, this worked for a string length of 100 but when I extended this to 150 it ended up looking like a bell curve again. 
I have no idea how I would fix this as it would have to be different for different length sizes.

A:

The correct formulas are
        x = Sin(Angle) * LengthOfString 
        y = Cos(Angle) * LengthOfString 

With  0 <= Angle <= 2*pi 

