Drawing a line

I am trying to make a basic shape drawing utility on my prog.

Currently it's for darwing a triangle.

The user puts in the 3 sides(lengths) and they are drawn on a form.

All I have done so far is Drawn 3 lines on a form and match there length labels to the text input from the user. To adjust the lengths of the lines I assume I need to work off some kind of scale.
Right now I have this for side A:

Line1.y1 = txtSideA.text
line1.y2 = txtSideA.text

obviously this is no good

Any tips? Ideas on a scale?

Thanks Much!