Draw a curve?

how can I draw this in a picturebox???
y=3x²+2x+4

Use a For Loop.

For X = 0 To PB.Width
'All values of pixels that fit nicely in the picturebox.
Y = 3 * X * X + 2 * X + 4
'Function.
GFXofPB.DrawLine(Pens.Black, Xold, Yold, X, Y)
'Draw a line connecting the two points.
Next

That'll just draw the positive part, and require a really tall textbox and a small width.
For drawing part of the functions for negative values and for scaling, you'll need two more X and Y variables to go with the X and Y above... use one pair to determine where the line point will be drawn and the other pair to determine what the actual values are going to be used for X and Y. :)

I discussed it in this thread (where I use GetPixel and SetPixel):
http://www.xtremevbtalk.com/showthread.php?t=101869&highlight=Plotting+function

P.S. For doing lines, you need to store the old position of the line, unless you use GFXtoPB.DrawLines() and store all of the function points into an array.

Thanks for that.
and one mor question
can I change coordinate system.
y values increase downwards
Is it posible to increase yvalues upwards. like real coordinate system

Oh... sure.
You can do something like this:

Pretend that Y is the result that you got from the function...
to make positive Y go up, you need to make Y negative. Then, if you add PB.Width, zero will be at the bottom of the picturebox. :)
GY = PB.Width - Y
That will put Y = 0 at the bottom of the textbox, and it will go to the top when Y increases. :)