Notes Class 9 Maths Chapter 4 Linear Equations in Two Variables

Notes For All Chapters Maths Class 9

1. 1. Linear Equations: Any equation which can be put in the form ax + by + c = 0, where a, b and c are real numbers and a and b are not both zero is called a linear equation in two variables.
      The solution of a linear equation is not affected when
      • the same number is added to (or subtracted from) both the sides of the equation.
      • you multiply or divide both the sides of the equation by the same non-zero number.
   2. A linear equation in two variables has infinitely many solutions.

1. The graph of every linear equation in two variables is a straight line.
2. x = 0 is the equation of the y-axis and y = 0 is the equation of the x-axis.
3. The graph of x = a is a straight line parallel to the y-axis.
4. The graph of y = a is a straight line parallel to the x-axis.
5. An equation of the type y = mx represents a line passing through the origin.
6. Every point on the graph of a linear equation in two variables is a solution of the linear equation. Moreover, every solution of the linear equation is a point on the graph of the linear equation.
7. Graph of a Linear Equation in Two Variables: We know that a linear equation in two variables has infinitely many solutions. We write the solutions as a pair of values and plot, these points on a graph paper and join them to get a line.