Class IX Math
Notes for Linear Equations in Two Variables
An equation of the form ax + by + c = 0 where a, b, c are real numbers, a ≠ 0, b ≠ 0 and x, y are variables is called a linear equation in two variable.
Anys pair of values ofxandywhich satisfies the equation ax + by + c = 0, wherea, b, c are non-zero real numbers, is called a solution of the equation
• A linear equation in two variables has infinitely many solutions.
• Every point on the graph of a linear equation in two variables is a solution of the equation.
Geometric representation of ax + c = 0 as an equation
• in one variable is
• in two variable is
a.x + 0.y = –c.
• If a ≠ 0, c ≠ 0 and b = 0.
The equation
ax +
by +
c �� 0 reduces to
ax +
c = 0 or
The graph is a straight line. Parallel to y-
axis and passing through the point
• If b ≠ 0, c ≠ 0 and a ≠ 0. The equation
ax +
by +
c = 0 reduces to
by +
c = 0 or
The graph is a straight line parallel to x axis and passing through the point
• If a ≠ 0, b ≠ 0, c = 0 . The equation ax + by + c = 0 reduces to ax = 0 i.e. x= 0. The graph is y-axis itself
• If a = 0, b ≠ 0, c = 0. The equation ax + by + c = 0 reduces to by = 0 i.e. y= 0. The graph is x-axis itself
• If c = 0 , the equation ax + by + c = 0 reduces to ax + by = 0. The graph is a line passing through origin.