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### What are linear equations?

A linear equation is an equation in which there are either one or two variables, the power (exponent) on each variable being only 1 (that's why it is called linear). No term in the equation contains the variable/s in the denominator. If there are two variables in a linear equation, the two variables are never multiplied together in a single term (because that would give the equation a degree of 2).

There are two types of linear equations:
1. Linear equations containing one variable
2. Linear equations containing two variables
A linear equation containing a single variable differs from one containing two variables in that it's graph is a single point, whereas the graph of a two-variable linear equation is a straight line.

### Identifying linear equations

After simplifying an equation, you can identify whether it is linear or not by the following rules:
1. There is either one or two variables in the equation
2. No variable is in the denominator of a fraction
3. No variable has a power (exponent) other than 1
4. If there are two variables, they are not present together in a single term
For example,
• 2x^2 - 1 = 0 is not a linear equation since the power on 'x' is 2
• x^3 + 3x^2 + 4x + 2 = 0 is not a linear equation since 'x' has a power of 3 and 2.
• 3/x + 4 = 5x is not a linear equation since 'x' is in the denominator.
• 3xy + 4x = 6y is not a linear equation since 'x' and 'y' are multiplied together in the first term.
On the other hand,
• x + y = 1 is a linear equation
• 2x + 4 = 1
• 3/x + 2 = 1 is a linear equation because on simplifying, we get 3 + 2x = x which has no 'x' in the denominator or a power greater than 1.

### LHS and RHS of a linear equation

A linear equation always has a = sign. The expression on the left of the = sign in an equation is called the LHS (Left Hand Side) and the expression on the right of the = sign is called the RHS (Right Hand Side).

For example, in the following equation,
2x + 4 = 5x + 3
the expression on the left of the = sign is 2x + 4 and hence it is the LHS, whereas the expression on the right of the = sign is 5x + 3 and is called the RHS.