Graphing Linear Equations in Two Variables

Any equation that can be represented in the form of ax + by + c =o, where a,b, and c are real numbers and a, b are not equivalent to 0 is known as a linear equation in two variables namely x and y. The solutions for such types of equations are a pair of values, one for x and one for y which makes the two sides of the equation equal. 

There are infinitely multiple solutions for linear equations in two variables. For example, x + 2y = 6 in a linear equation and its solutions are (0,3), (6,0), (2,2) because they  satisfy the equation x + 2y = 6.

Linear Equation in Two Variables Example

Here, we will understand the linear equation in two variables through an example

Let us take the equation

5x + 3y = 30

The above equation has two variables i.e. x and y

This equation can be represented graphically through substituting the variables equals zero.

The value of x, when y equals to zero is

5x + 3(0) = 30

→ x = 6

And, the value of y when x equals to zero is

5 (0) + 3y = 30

Y = 10

(image will be uploaded soon)

Graphing of Linear Equation in Two Variables

As the solutions of linear equations in two variables is a pair of numbers (x,y), we can express the solutions in a coordinate plane.

Let us understand the concept by considering the equation given below:

2x + y =  6     (1)

Some of the solution of the equations given above are:

(0,6), (3,0), (1,4) ,(2,2) because they satisfy the equation 2x + y =  6 

We can Represent the Equation (1) in Tabulated Form in the Following Manner:

Now, we are plotting the above coordinates in the coordinate plane below.

We can take any two of the coordinates and join them to form a line. Let that line be PQ. It can be seen in the below figure that all the 4 coordinates are lying on the same line PQ.

Let us take any other point such as ( 4,-2) which lies on the line PQ. 

Now, we will verify whether the above point is satisfying the equation or not.

Substituting the point ( 4,-2) in equation (1) we get,

LHS = ( 2*4) -2 = 6 = RHS

Hence verified.

Therefore, the coordinate (4,-2) is solution of 2x + y =  6 

Similarly, if we will take any other points, it will also satisfy the equation 2x + y =  6 

Note:

• It can be seen that all the points lie on the line PQ provide a solution of 2x + y =  6 

• All the solution of 2x + y =  6  lies on the line PQ

• Coordinates that will not satisfy the equation of 2x + y =  6  will not lie in the line PQ.

Important points of graphing of linear equation in two variables

We can conclude the following points, for a linear equation in two variables

• Each point on the line will be the solution to the equation.

• Each solution of the equation will be some point on the line

Hence, we can represent every linear equation in two variables in a graph as a straight line in a coordinate plane. Points on the lines are known as the solution of the equation. Due to this, an equation with one degree is known as linear equations. The expression of linear equations in a graph is known as graphing of linear equations in two variables.

Solved Examples:

1. 10 students of class 9th took part in a Science quiz. If the number of girls participated in a  quiz is 4 times more than boys, find the number of girls and boys who took part in a Science quiz.

Solution: Let the number of boys participated by y and the number of girls participated by x.

Accordingly, equation will be

x + y = 10  (1)

y = x + 4  (2)

Let us now represent the above equations 1 and 2  graphically by calculating 2 solutions for each of the equations. The two solutions of the equations are:

x + y = 10 → y = 10 - x 

x + y =  4  

Now we will plot the above points in a graph,

We will draw two lines AB and CE passing through the points to represent the equation

The two lines AB and CE will intersect at point E ( 3, 7). 

Hence, x = 3 and y = 7 is the required solution of the pair of linear equations.

So, the total number of boys participated in quiz = 3  and the total number of girls participated in the quiz = 7

Verification

Substituting the values of x =3 and y= 7 in the equation (1) , we get

L.H.S = 3 + 7= 10

LHS = RHS

Hence verified

Substituting the values of x =3 and y= 7 in the equation (2) , we get

7 = 3 + 4

LHS = RHS

Hence verified

2. Represent graphically that the following system of equation 2x + 3y = 10 and 4x + 6y = 2 has no solution.

Solution: The given equations are:

2x + 3y = 10 → y = (10 - 2x) /3

4x + 6y = 2 → y = (12 - 4x) /6

No, we are plotting the points A ( -4,6) and B (2,2) in a graph. Join these two points to form a line AB.

Also, plot the points C ( -3,4) and D ( 3,0) and join them to form a line CD

Now, you can see the lines in the graph are parallel to each other. As the line has no common points, there will be no common solution. 

Therefore, the given system of the equation has no solution

Quiz Time

1. The graph of x= -2 in a line parallel to the

1. X- axis

2. Y -axis

3. Both x and y- axis

4. None of these

2. If the lines represented by 2x + ky = 1 and 3x - 5y = 7 ae parallel, then value of k is

1. -10/3

2. 10/3

3. -13

4. -7

3.  What will be the representation of the line, if the pair of equations is consistent?

1. parallel

2. Always intersecting

3. Always consistent

4. Two solutions