# Introduction

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In the earlier classes, you have come across several **algebraic expressions** and **equations**. Some examples of expressions we have so far worked with are:

**5x, 2x – 3, 3x + y, 2xy + 5, xyz + x + y + z, **

Some examples of equations are: **5x = 25, 2x – 3 = 9,2y+ **

You would remember that equations use the equality (=) sign; it is missing in expressions.

Of these given expressions, many have more than one variable. For example, 2xy + 5 has

We however, restrict to **expressions with only one variable when we form equations**. Moreover, **the expressions we use to form equations are linear**. This means that the highest power of the variable appearing in the expression is

These are linear expressions:

**2x, 2x + 1, 3y – 7, 12 – 5z, **

These are **not** linear expressions:

Here we will deal with equations with linear expressions in one variable only. Such equations are known as **linear equations in one variable.** The simple equations which you studied in the earlier classes were all of this type.

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Let us briefly revise what we know:

**(a)** An algebraic equation is an equality involving variables. It has an equality sign. The expression on the left of the equality sign is the **Left Hand Side (LHS)**. The expression on the right of the equality sign is the **Right Hand Side (RHS).**

**(b)** In an equation the values of the expressions on the LHS and RHS are of the equation.

**(c)** How to find the solution of an equation? **We assume that the two sides of the equation are balanced.** We perform the same mathematical operations on both sides of the equation, so that the balance is not disturbed. A few such steps give the solution.