An equation is nothing but a statement that defines the equality between two or more expressions. The equation is denoted by the ‘equal to’ sign. The part of the equation towards the left side is known as the lefthand side (LHS), and the part inclined towards the right is (RHS) righthand side. An equation contains both variables as well as constant. Both need not be present, but one of these mathematical terms is vital for forming an equation.
For example, 20a + 3c = 12, this is an ideal example of an equation. Here ‘a’ and ‘c’ are known as the variable, and ‘12’ is known as the constant of this equation. 20a + 3c is the LHS of the equation, while 12 is the RHS. It must be noted that the same mathematical operations are carried out on both sides of the equation. This is one of the most important rules for solving an equation. If, for instance, you want to multiply the LHS by two, then the RHS shall also be multiplied by 2. This ensures that the equation always remains the same.
Now that we have a basic understanding of an equation let us look into different types of equations in mathematics. The equations are categorized as linear or nonlinear equations based on the degree and variable in the equations.
Degree of an equation: The maximum power of the variable in the algebraic statement is the degree of polynomials in one variable. For instance, consider the following equation: x3 + 11x + 21. The equation's degree is three, which is the largest power of the variable in the equation.
The difference between the two types of equations is tabulated below:










NCERT Class 9 Maths Chapter 4 Linear Equations in Two Variables is one of the most important chapters in Class 9, it extensively talks about linear equations, nonlinear equations, the difference between them, and other important theorems.