Maths

PAIR OF LINEAR EQUATIONS IN TWO VARIABLES 69
3.6 Summary
In this chapter, you have studied the following points:
1. Two linear equations in the same two variables are called a pair of linear equations in two
variables. The most general form of a pair of linear equations is
a 1
x + b 1
y + c 1
= 0
a 2
x + b 2
y + c 2
= 0
2 2 2 2
1 1 2 2
where a 1
, a 2
, b 1
, b 2
, c 1
, c 2
are real numbers, such that a b 0, a b 0.
✁ ✁
2. A pair of linear equations in two variables can be represented, and solved, by the:
(i) graphical method
(ii) algebraic method
3. Graphical Method :
The graph of a pair of linear equations in two variables is represented by two lines.
(i) If the lines intersect at a point, then that point gives the unique solution of the two
equations. In this case, the pair of equations is consistent.
(ii) If the lines coincide, then there are infinitely many solutions — each point on the
line being a solution. In this case, the pair of equations is dependent (consistent).
(iii) If the lines are parallel, then the pair of equations has no solution. In this case, the
pair of equations is inconsistent.
4. Algebraic Methods : We have discussed the following methods for finding the solution(s)
of a pair of linear equations :
(i) Substitution Method
(ii) Elimination Method
(iii) Cross-multiplication Method
5. If a pair of linear equations is given by a 1
x + b 1
y + c 1
= 0 and a 2
x + b 2
y + c 2
= 0, then the
following situations can arise :
(i)
(ii)
a
a
b
✂ : In this case, the pair of linear equations is consistent.
b
1 1
2 1
a1 b1 c1
☎ ✄ : In this case, the pair of linear equations is inconsistent.
a b c
2 2 2
a1 b1 c1
(iii)
: In ✆ this ✆ case, the pair of linear equation is dependent and consistent.
a2 b2 c2
6. There are several situations which can be mathematically represented by two equations
that are not linear to start with. But we alter them so that they are reduced to a pair of
linear equations.