1. An algebraic equation is an equality involving variables. It says that the value of the expression on one side of the equality sign is equal to the value of the expression on the other side.

2. The equations we study in previous classes and this class are linear equations in one variable .In such equations, the expressions which form the equation contain only one variable. Further, the equations are linear, i.e. the highest power of the variable appearing in the equation is 1.

3. A linear equation may have for its solution any rational equation. 

4. An equation may have linear expressions on both sides. Equations that we studied in classes VI and VII had just a number on one side  of the equation. But in NCERT  Maths class 8 Chapter 2 we learnt the equation with the variable in both sides.
5. Just as numbers, variables can, also  be transposed from one side of the equation to the other.

6. Occasionally, the expressions forming equations have to be simplified before we can solve them by usual methods.  Some equations may not even be linear to begin with, but they can be brought to a linear form by multiplying both sides of the equation by a suitable expression .

7. The utility of linear equations is in their diverse applications; different problems on numbers, ages, perimeters, combination of currency notes, and so on can be solved using linear equations.