Linear Equations:

Consider the following equation:
               2x + 5 = 0
Its solution, i.e., the root of the equation, is -5/2.

While solving an equation, you must always keep the following points in mind:
The solution of a linear equation is not affected when:
(i) the same number is added to (or subtracted from) both the sides of the equation.
(ii) you multiply or divide both the sides of the equation by the same non-zero
number.

Let us now consider the following situation:
In a One-day International Cricket match between India and Sri Lanka played in
Nagpur, two Indian batsmen together scored 176 runs. Express this information in the
form of an equation.
Here, you can see that the score of neither of them is known, i.e., there are two
unknown quantities. Let us use x and y to denote them. So, the number of runs scored
by one of the batsmen is x, and the number of runs scored by the other is y. We know
that,
               x + y = 176,
which is the required equation.
This is an example of a linear equation in two variables. It is customary to denote
the variables in such equations by x and y, but other letters may also be used. Some
examples of linear equations in two variables are:
               1.2s + 3t = 5,

               p + 4q = 7,

               5s + 2t = 7 and

               2x - 7y = 3.
Note that you can put these equations in the form 1.2s + 3t – 5 = 0,
p + 4q – 7 = 0, 5s + 2t – 7 = 0 and 2x – 7y – 3 = 0, respectively.
So, any equation which can be put in the form ax + by + c = 0, where a, b and c
are real numbers, and a and b are not both zero, is called a linear equation in two
variables. This means that you can think of many such equations.