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EXAMPLE:1 Find the solution of the equation 4x = 12 by the trial-and-error method.
12 Linear Equations in SOLUTION We try several values of x and find the values of the LHS and the RHS. We stop when for a

particular value of x, LHS = RHS.
One Variable x LHS RHS

1 4 × 1 = 4 12
In arithmetic, we usually come across statements of the following type: 2 4 × 2 = 8 12
(i) 16+5=21 3 4 × 3 = 12 12
(ii) 7 × (5 + 4) = 7 × 5 + 7 × 4, etc.
Such a statement involving the symbol ‘=’ is called a statement of equality or simply an
equality. x = 3 is the solution of the given equation.

Clearly, none of the above statements involves a variable. EXAMPLE:2 Solve the equation 3x - 5 = 7 - x by the trial-and-error method.
SOLUTION We try several values of x and find the values of the LHS and the RHS. We stop when
EQUATION A statement of equality which involves one or more variables is called an equation. for a particular value of x, LHS = RHS.
Consider the following statements:
(i) A number x increased by 7 is 15. x LHS RHS
(ii) 9 exceeds a number x by 3. 1 3 × l-5=-2 7 -1 =6
(iii) 4 times a number x is 24. 2 3 × 2-5=1 7 - 2=5
(iv) A number y divided by 5 is 7.
(v) The sum of the number x and twice the number y is 12. 3 3 × 3-.5=4 7- =4
We can write the above statements as under: :. x = 3 is the solution of the given equation.
(i) x+7=15 (ii) 9 - x = 3 (iii) 4x=24 EXAMPLE:3 Solve the equation 1 y + 5 = 8 by the trial-and-error method.
(iv) y=7 3
5 SOLUTION We make a guess and try several values of y, and fmd the values of the LHS as well as
Clearly, each one of the above statements is a statement of equality, containing one or more variables. Thus, each the RHS in each case. We stop when for a particular value of y, LHS = RHS.
one of them is an equation.
Y LHS RHS
Each of the equations through (i) to (iv) involves only one unknown (i.e., variable), while the equation (v) con- 3 1 3 x 6 + 5 = 7 7 -1 = 6
tains two unknowns, namely, x and y. 6 1 3 x 3 + 5 = 6 7 - 2 = 5

9 1 x 9 + 5 = 8 7 - = 4
LINEAR EQUATION An equation in which the highest power of the variables involved is 1 is called a linear 3
equation. Thus, when y = 9, we have: LHS = RHS.
In this chapter, we shall discuss the linear equations in one variable only. :. y = 9 is the solution of the given equation.

Clearly, the sign of equality in an equation divides it into two sides, namely, the left-hand side and the right-hand
side, written as LHS and RHS respectively.

SOLU TION OF AN EQUATION A number which makes LHS = RHS when it is substitutedfor the
variable in an equation is said to satisfy the equation and is called a solution or root of the equation.
Solving an equation is finding the roots of the equation.

SOLVING A LINEAR EQUATION BY THE TRIAL-AND-ERROR METHOD In this method, we often
make a guess of the root of the equation. We try several values of the variables and find the values of the LHS and
the RHS in each case. When LHS = RHS for a particular value of the variable we say that it is a root of the equa-
tion.