the elimination and substitution method

1. Linear Equation in Two
Variables

2. Linear Equations
Definition of a Linear Equation
A linear equation in two variable x is an
equation that can be written in the form ax +
by + c = 0, where a ,b and c are real numbers
and a and b is not equal to 0.
An example of a linear equation in x is .

3. Equations of the form ax + by = c are called
linear equations in two variables.
The point (0,4) is the y-intercept.
The point (6,0) is the x-intercept.
x
2
-2
This is the graph of the
equation 2x + 3y = 12.
(0,4)
(6,0)

4. Example:
Given the equation 2x + 3y = 18, determine if the
ordered pair (3, 4) is a solution to the equation.
We substitute 3 in for x and 4 in for y.
2(3) + 3 (4) ? 18
6 + 12 ? 18
18 = 18 True.
Therefore, the ordered pair (3, 4) is a solution to the
equation 2x + 3y = 18.
Solution of an Equation in Two Variables

5. The Rectangular Coordinate System
Each point in the rectangular coordinate system corresponds to an ordered pair of
real numbers (x,y). Note the word “ordered” because order matters. The first
number in each pair, called the x-coordinate, denotes the distance and direction
from the origin along the x-axis. The second number, the y-coordinate, denotes
vertical distance and direction along a line parallel to the y-axis or along the y-axis
Itself.
In plotting points,
we move across first
(either left or right), and
then move either up or
down, always starting
from the origin.
Point Movement from origin
(3.5) 3 units right and 5 units up
(4,-3) 4 units right and 3 units down
(-2,-7) 2 units left and 7 units down
(0,0) 0 right or left and 0 up or down

6. The Rectangular Coordinate System
In the rectangular coordinate system,
the horizontal number line is the x-axis.
The vertical number line is the y-axis.
The point of intersection of these axes is
their zero points, called the origin. The
axes divide the plane into 4 quarters,
called quadrants.

7. CARTESIAN PLANE
x- axis
y-axis
Quadrant I
(+,+)
Quadrant II
( - ,+)
Quadrant IV
(+, - )
Quadrant III
( - , - )

8. Plotting Points
EXAMPLE
SOLUTION
Plot the points (3,2) and (-2,-4).

 (3,2)
(-2,-4)

9. The Graph of an Equation
The graph of an equation in two variables is the set of
points whose coordinates satisfy the equation.
An ordered pair of real numbers (x,y)
is said to satisfy the equation when substitution of the x and y
coordinates into the equation makes it a true statement.

10. Let ax + by +c = O , where a ,b , c are
real numbers such that a and b ≠ O.
Then, any pair of values of x and y
which satisfies the equation ax + by +c
= O, is called a solution of it.

11. Find five solutions to the equation y = 3x + 1.
Start by choosing some x values and then computing the
corresponding y values.
If x = -2, y = 3(-2) + 1 = -5. Ordered pair (-2, -5)
If x = -1, y = 3(-1) + 1 = -2. Ordered pair ( -1, -2)
If x =0, y = 3(0) + 1 = 1. Ordered pair (0, 1)
If x =1, y = 3(1) + 1 =4. Ordered pair (1, 4)
If x =2, y = 3(2) + 1 =7. Ordered pair (2, 7)
Finding Solutions of an Equation

12. Plot the five ordered pairs to obtain the graph of y = 3x + 1
(2,7)
(1,4)
(0,1)
(-1,-2)
(-2,-5)
Graph of the Equation

13. TYPES OF METHOD:-
TO SOLVE A PAIR OF LINEAR
EQUATION IN TWO VARIABLE

14. • The method of substitution is not preferable if none of the
coefficients of x and y are 1 or -1. For example, substitution is
not the preferred method for the system below:
2x – 7y = 3
-5x + 3y = 7
• A better method is elimination by addition. The following
operations can be used to produce equivalent systems:
– 1. Two equations can be interchanged.
– 2. An equation can be multiplied by a non-zero constant.
– 3. An equation can be multiplied by a non-zero constant
and then added to another equation.

15. SUBSTITUTION METHOD:
The first step to solve a pair of linear equations by the
substitution method is to solve one equation for either of the
variables. The choice of equation or variable in a given pair does
not affect the solution for the pair of equations.
In the next step, we’ll substitute the resultant value of one
variable obtained in the other equation and solve for the other
variable.
In the last step, we can substitute the value obtained of the
variable in any one equation to find the value of the second
variable