Page 1
1
· Methods of solving linear equations in two variables - graphical method,
Cramer’s method
· Equations that can be transformed in linear equation in two variables
· Application of simultaneous equations
Let’s recall.
Linear equation in two variables
An equation which contains two variables and the degree of each term
containing variable is one, is called a linear equation in two variables.
ax + by + c = 0 is the general form of a linear equation in two variables;
a, b, c are real numbers and a, b are not equal to zero at the same time.
Ex. 3x - 4y + 12 = 0 is the general form of equation 3x = 4y - 12
Activity : Complete the following table
No. Equation Is the equation a linear equation in 2
variables ?
1
4m + 3n = 12
Yes
2
3x
2
- 7y = 13
3
2 x - 5 y = 16
4
0x + 6y - 3 = 0
5
0.3x + 0y -36 = 0
6
45
4
xy
7
4xy - 5y - 8 = 0
1
Linear Equations in Two Variables
Let’s study.
Page 2
1
· Methods of solving linear equations in two variables - graphical method,
Cramer’s method
· Equations that can be transformed in linear equation in two variables
· Application of simultaneous equations
Let’s recall.
Linear equation in two variables
An equation which contains two variables and the degree of each term
containing variable is one, is called a linear equation in two variables.
ax + by + c = 0 is the general form of a linear equation in two variables;
a, b, c are real numbers and a, b are not equal to zero at the same time.
Ex. 3x - 4y + 12 = 0 is the general form of equation 3x = 4y - 12
Activity : Complete the following table
No. Equation Is the equation a linear equation in 2
variables ?
1
4m + 3n = 12
Yes
2
3x
2
- 7y = 13
3
2 x - 5 y = 16
4
0x + 6y - 3 = 0
5
0.3x + 0y -36 = 0
6
45
4
xy
7
4xy - 5y - 8 = 0
1
Linear Equations in Two Variables
Let’s study.
2
Simultaneous linear equations
When we think about two linear equations in two variables at the same
time, they are called simultaneous equations.
Last year we learnt to solve simultaneous equations by eliminating one
variable. Let us revise it.
Ex. (1) Solve the following simultaneous equations.
(1) 5x - 3y = 8; 3x + y = 2
Solution :
Method I : 5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Multiplying both sides of
equation (II) by 3.
9x + 3y = 6 . . . (III)
5x - 3y = 8. . . (I)
Now let us add equations (I)
and (III)
5x - 3y = 8
9x + 3y = 6
14x = 14
\ x = 1
substituting x = 1 in equation (II)
3x + y = 2
\ 3 ´ 1 + y = 2
\ 3 + y = 2
\ y = -1
solution is x = 1, y = -1; it is also
written as (x, y) = (1, -1)
Method (II)
5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Let us write value of y in terms
of x from equation (II) as
y = 2 - 3x . . . (III)
Substituting this value of y in
equation (I).
5x - 3y = 8
\ 5x - 3(2 - 3x) = 8
\ 5x - 6 + 9x = 8
\ 14x - 6 = 8
\ 14x = 8 + 6
\ 14x = 14
\ x = 1
Substituting x = 1 in equation
(III).
y = 2 - 3x
\ y = 2 - 3 ´ 1
\ y = 2 - 3
\ y = -1
x = 1, y = -1 is the solution.
+
Page 3
1
· Methods of solving linear equations in two variables - graphical method,
Cramer’s method
· Equations that can be transformed in linear equation in two variables
· Application of simultaneous equations
Let’s recall.
Linear equation in two variables
An equation which contains two variables and the degree of each term
containing variable is one, is called a linear equation in two variables.
ax + by + c = 0 is the general form of a linear equation in two variables;
a, b, c are real numbers and a, b are not equal to zero at the same time.
Ex. 3x - 4y + 12 = 0 is the general form of equation 3x = 4y - 12
Activity : Complete the following table
No. Equation Is the equation a linear equation in 2
variables ?
1
4m + 3n = 12
Yes
2
3x
2
- 7y = 13
3
2 x - 5 y = 16
4
0x + 6y - 3 = 0
5
0.3x + 0y -36 = 0
6
45
4
xy
7
4xy - 5y - 8 = 0
1
Linear Equations in Two Variables
Let’s study.
2
Simultaneous linear equations
When we think about two linear equations in two variables at the same
time, they are called simultaneous equations.
Last year we learnt to solve simultaneous equations by eliminating one
variable. Let us revise it.
Ex. (1) Solve the following simultaneous equations.
(1) 5x - 3y = 8; 3x + y = 2
Solution :
Method I : 5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Multiplying both sides of
equation (II) by 3.
9x + 3y = 6 . . . (III)
5x - 3y = 8. . . (I)
Now let us add equations (I)
and (III)
5x - 3y = 8
9x + 3y = 6
14x = 14
\ x = 1
substituting x = 1 in equation (II)
3x + y = 2
\ 3 ´ 1 + y = 2
\ 3 + y = 2
\ y = -1
solution is x = 1, y = -1; it is also
written as (x, y) = (1, -1)
Method (II)
5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Let us write value of y in terms
of x from equation (II) as
y = 2 - 3x . . . (III)
Substituting this value of y in
equation (I).
5x - 3y = 8
\ 5x - 3(2 - 3x) = 8
\ 5x - 6 + 9x = 8
\ 14x - 6 = 8
\ 14x = 8 + 6
\ 14x = 14
\ x = 1
Substituting x = 1 in equation
(III).
y = 2 - 3x
\ y = 2 - 3 ´ 1
\ y = 2 - 3
\ y = -1
x = 1, y = -1 is the solution.
+
3
Ex. (2) Solve : 3x + 2y = 29; 5x - y = 18
Solution : 3x + 2y = 29. . . (I) and 5x - y = 18 . . . (II)
Let’s solve the equations by eliminating ’y’. Fill suitably the boxes below.
Multiplying equation (II) by 2.
\ 5x ´ - y ´ = 18 ´
\ 10x - 2y = . . . (III)
Let’s add equations (I) and (III)
3x + 2y = 29
+
- =
= \ x =
Substituting x = 5 in equation (I)
3x + 2y = 29
\ 3 ´ + 2y = 29
\ + 2y = 29
\ 2y = 29 -
\ 2y = \ y =
(x, y) = ( , ) is the solution.
Ex. (3) Solve : 15x + 17y = 21; 17x + 15y = 11
Solution : 15x + 17y = 21. . . (I)
17x + 15y = 11 . . . (II)
In the two equations above, the coefficients of x and y are interchanged.
While solving such equations we get two simple equations by adding and
subtracting the given equations. After solving these equations, we can easily find
the solution.
Let’s add the two given equations.
15x + 17y = 21
17x + 15y = 11
32x + 32y = 32
+
Page 4
1
· Methods of solving linear equations in two variables - graphical method,
Cramer’s method
· Equations that can be transformed in linear equation in two variables
· Application of simultaneous equations
Let’s recall.
Linear equation in two variables
An equation which contains two variables and the degree of each term
containing variable is one, is called a linear equation in two variables.
ax + by + c = 0 is the general form of a linear equation in two variables;
a, b, c are real numbers and a, b are not equal to zero at the same time.
Ex. 3x - 4y + 12 = 0 is the general form of equation 3x = 4y - 12
Activity : Complete the following table
No. Equation Is the equation a linear equation in 2
variables ?
1
4m + 3n = 12
Yes
2
3x
2
- 7y = 13
3
2 x - 5 y = 16
4
0x + 6y - 3 = 0
5
0.3x + 0y -36 = 0
6
45
4
xy
7
4xy - 5y - 8 = 0
1
Linear Equations in Two Variables
Let’s study.
2
Simultaneous linear equations
When we think about two linear equations in two variables at the same
time, they are called simultaneous equations.
Last year we learnt to solve simultaneous equations by eliminating one
variable. Let us revise it.
Ex. (1) Solve the following simultaneous equations.
(1) 5x - 3y = 8; 3x + y = 2
Solution :
Method I : 5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Multiplying both sides of
equation (II) by 3.
9x + 3y = 6 . . . (III)
5x - 3y = 8. . . (I)
Now let us add equations (I)
and (III)
5x - 3y = 8
9x + 3y = 6
14x = 14
\ x = 1
substituting x = 1 in equation (II)
3x + y = 2
\ 3 ´ 1 + y = 2
\ 3 + y = 2
\ y = -1
solution is x = 1, y = -1; it is also
written as (x, y) = (1, -1)
Method (II)
5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Let us write value of y in terms
of x from equation (II) as
y = 2 - 3x . . . (III)
Substituting this value of y in
equation (I).
5x - 3y = 8
\ 5x - 3(2 - 3x) = 8
\ 5x - 6 + 9x = 8
\ 14x - 6 = 8
\ 14x = 8 + 6
\ 14x = 14
\ x = 1
Substituting x = 1 in equation
(III).
y = 2 - 3x
\ y = 2 - 3 ´ 1
\ y = 2 - 3
\ y = -1
x = 1, y = -1 is the solution.
+
3
Ex. (2) Solve : 3x + 2y = 29; 5x - y = 18
Solution : 3x + 2y = 29. . . (I) and 5x - y = 18 . . . (II)
Let’s solve the equations by eliminating ’y’. Fill suitably the boxes below.
Multiplying equation (II) by 2.
\ 5x ´ - y ´ = 18 ´
\ 10x - 2y = . . . (III)
Let’s add equations (I) and (III)
3x + 2y = 29
+
- =
= \ x =
Substituting x = 5 in equation (I)
3x + 2y = 29
\ 3 ´ + 2y = 29
\ + 2y = 29
\ 2y = 29 -
\ 2y = \ y =
(x, y) = ( , ) is the solution.
Ex. (3) Solve : 15x + 17y = 21; 17x + 15y = 11
Solution : 15x + 17y = 21. . . (I)
17x + 15y = 11 . . . (II)
In the two equations above, the coefficients of x and y are interchanged.
While solving such equations we get two simple equations by adding and
subtracting the given equations. After solving these equations, we can easily find
the solution.
Let’s add the two given equations.
15x + 17y = 21
17x + 15y = 11
32x + 32y = 32
+
4
Dividing both sides of the equation by 32.
x + y = 1 . . . (III)
Now, let’s subtract equation (II) from (I)
15x + 17y = 21
17x + 15y = 11
-2x + 2y = 10
dividing the equation by 2.
-x + y = 5 . . . (IV)
Now let’s add equations (III) and (V).
x + y = 1
-x + y = 5
\ 2y = 6 \ y = 3
Place this value in equation (III).
x + y = 1
\ x + 3 = 1
\ x = 1 - 3 \ x = -2
(x, y) = (-2, 3) is the solution.
- - -
Practice Set 1.1
(1) Complete the following activity to solve the simultaneous equations.
5x + 3y = 9 -----(I)
-
+
+
2x - 3y = 12 ----- (II)
Let’s add eqations (I) and (II).
5x + 3y = 9
2x - 3y = 12
x =
x = x =
Place x = 3 in equation (I).
5 ´ + 3y = 9
3y = 9 -
3y =
y =
3
y =
\ Solution is (x, y) = ( , ).
Page 5
1
· Methods of solving linear equations in two variables - graphical method,
Cramer’s method
· Equations that can be transformed in linear equation in two variables
· Application of simultaneous equations
Let’s recall.
Linear equation in two variables
An equation which contains two variables and the degree of each term
containing variable is one, is called a linear equation in two variables.
ax + by + c = 0 is the general form of a linear equation in two variables;
a, b, c are real numbers and a, b are not equal to zero at the same time.
Ex. 3x - 4y + 12 = 0 is the general form of equation 3x = 4y - 12
Activity : Complete the following table
No. Equation Is the equation a linear equation in 2
variables ?
1
4m + 3n = 12
Yes
2
3x
2
- 7y = 13
3
2 x - 5 y = 16
4
0x + 6y - 3 = 0
5
0.3x + 0y -36 = 0
6
45
4
xy
7
4xy - 5y - 8 = 0
1
Linear Equations in Two Variables
Let’s study.
2
Simultaneous linear equations
When we think about two linear equations in two variables at the same
time, they are called simultaneous equations.
Last year we learnt to solve simultaneous equations by eliminating one
variable. Let us revise it.
Ex. (1) Solve the following simultaneous equations.
(1) 5x - 3y = 8; 3x + y = 2
Solution :
Method I : 5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Multiplying both sides of
equation (II) by 3.
9x + 3y = 6 . . . (III)
5x - 3y = 8. . . (I)
Now let us add equations (I)
and (III)
5x - 3y = 8
9x + 3y = 6
14x = 14
\ x = 1
substituting x = 1 in equation (II)
3x + y = 2
\ 3 ´ 1 + y = 2
\ 3 + y = 2
\ y = -1
solution is x = 1, y = -1; it is also
written as (x, y) = (1, -1)
Method (II)
5x - 3y = 8. . . (I)
3x + y = 2 . . . (II)
Let us write value of y in terms
of x from equation (II) as
y = 2 - 3x . . . (III)
Substituting this value of y in
equation (I).
5x - 3y = 8
\ 5x - 3(2 - 3x) = 8
\ 5x - 6 + 9x = 8
\ 14x - 6 = 8
\ 14x = 8 + 6
\ 14x = 14
\ x = 1
Substituting x = 1 in equation
(III).
y = 2 - 3x
\ y = 2 - 3 ´ 1
\ y = 2 - 3
\ y = -1
x = 1, y = -1 is the solution.
+
3
Ex. (2) Solve : 3x + 2y = 29; 5x - y = 18
Solution : 3x + 2y = 29. . . (I) and 5x - y = 18 . . . (II)
Let’s solve the equations by eliminating ’y’. Fill suitably the boxes below.
Multiplying equation (II) by 2.
\ 5x ´ - y ´ = 18 ´
\ 10x - 2y = . . . (III)
Let’s add equations (I) and (III)
3x + 2y = 29
+
- =
= \ x =
Substituting x = 5 in equation (I)
3x + 2y = 29
\ 3 ´ + 2y = 29
\ + 2y = 29
\ 2y = 29 -
\ 2y = \ y =
(x, y) = ( , ) is the solution.
Ex. (3) Solve : 15x + 17y = 21; 17x + 15y = 11
Solution : 15x + 17y = 21. . . (I)
17x + 15y = 11 . . . (II)
In the two equations above, the coefficients of x and y are interchanged.
While solving such equations we get two simple equations by adding and
subtracting the given equations. After solving these equations, we can easily find
the solution.
Let’s add the two given equations.
15x + 17y = 21
17x + 15y = 11
32x + 32y = 32
+
4
Dividing both sides of the equation by 32.
x + y = 1 . . . (III)
Now, let’s subtract equation (II) from (I)
15x + 17y = 21
17x + 15y = 11
-2x + 2y = 10
dividing the equation by 2.
-x + y = 5 . . . (IV)
Now let’s add equations (III) and (V).
x + y = 1
-x + y = 5
\ 2y = 6 \ y = 3
Place this value in equation (III).
x + y = 1
\ x + 3 = 1
\ x = 1 - 3 \ x = -2
(x, y) = (-2, 3) is the solution.
- - -
Practice Set 1.1
(1) Complete the following activity to solve the simultaneous equations.
5x + 3y = 9 -----(I)
-
+
+
2x - 3y = 12 ----- (II)
Let’s add eqations (I) and (II).
5x + 3y = 9
2x - 3y = 12
x =
x = x =
Place x = 3 in equation (I).
5 ´ + 3y = 9
3y = 9 -
3y =
y =
3
y =
\ Solution is (x, y) = ( , ).
5
2. Solve the following simultaneous equations.
(1) 3a + 5b = 26; a + 5b = 22 (2) x + 7y = 10; 3x - 2y = 7
(3) 2x - 3y = 9; 2x + y = 13 (4) 5m - 3n = 19; m - 6n = -7
(5) 5x + 2y = -3; x + 5y = 4 (6)
1
3
10
3
xy ;
2
1
4
11
4
xy
(7) 99x + 101y = 499; 101x + 99y = 501
(8) 49x - 57y = 172; 57x - 49y = 252
Let’s recall.
Graph of a linear equation in two variables
In the 9
th
standard we learnt that the graph of a linear equation in two
variables is a straight line. The ordered pair which satisfies the equation is a
solution of that equation. The ordered pair represents a point on that line.
Ex. Draw graph of 2x - y = 4.
Solution : To draw a graph of the equation let’s write 4 ordered pairs.
x 0 2 3 -1
y -4 0 2 -6
(x, y) (0, -4) (2, 0) (3, 2) (-1, -6)
To obtain ordered pair by
simple way let’s take x = 0
and then y = 0.
Scale : on both axes
1 cm = 1 unit.
-1 1
1
2
2
3 4 5 6 7 8 9
0
-1
-2
-2
-3
-3
-4
-4
-5
-5
-6
(3, 2)
(2, 0)
(0, -4)
(-1, -6)
X
X'
Y
Y'
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