Private Function F(ByVal X As Currency) As Currency
F = X*X
End Function
For X = -20 To 20
Y = F(X)
You can draw Y here with whatever graphics you need
Preferably a DrawPixel of some sort at (X, Y), however
it will be upside down, so youd have to take your Y
value and negate it.
Y = -Y
Then you need to move it on the visible area of the form.
Y += Width
Where Width is the width of the area that you want to
see the drawing at.
Next