NCERT Class 9 Mathematics Textbook for Blind Students made Screen Readable by Professor T K Bansal.

In earlier classes, we have studied linear equations in one variable. Can we now write down a linear equation in one variable? We may say that x + 1 = 0, x + √2 = 0 and √2 y + √3 = 0 are some examples of linear equations in one variable. We also know that such equations have a unique (one and only one) solution. We may also remember how to represent the solution on a number line. In this chapter, the knowledge of linear equations in one variable shall be recalled and extended to that of two variables. We will be considering questions like:
Does a linear equation in two variables have a solution?
If yes, is it unique?
What does the solution look like on the Cartesian plane?

We shall also be using the concepts we studied in Chapter 3 to answer these questions.