How to draw a line using y = mx +b in java?

Question

So I have a program that solves a system of linear equations, but that is not relevant. So what happens is that my program pass two linear equations in the form of: y = mx +b. I

Answer 1

When you draw a line in code, you need to draw from point A to point B. (a line segment)

Pick a point A to start the line from, then draw from A to (A.X + dx, A.Y + m * dx), where dx is the desired width of the line.

For example, you may want A to be one corner of your area, and dx to be the width of the area.