In Mathematics, you must have learned about different types of equations. Here, we are going to discuss the difference between linear and nonlinear equations. The difference between them is described here with the help of definitions and examples.
We come across a lot of equations while solving maths problems. Some equations include only numbers and some consist of only variables while others consist of both numbers and variables. Linear and nonlinear equations usually consist of numbers and variables.
Definition of Linear and NonLinear Equation
Linear means something related to a line. All the linear equations are used to construct a line. A nonlinear equation is such which does not form a straight line. It looks like a curve in a graph and has a variable slope value.
The major difference between linear and nonlinear equations is given here for the students to understand it in a more natural way. The differences are provided in a tabular form with examples.
What is the difference between Linear and Nonlinear Equations?
To find the difference between the two equations, i.e. linear and nonlinear, one should know the definitions for them. So, let us define and see the difference between them.
Linear Equations 
NonLinear Equations 
It forms a straight line or represents the equation for the straight line  It does not form a straight line but forms a curve. 
It has only one degree. Or we can also define it as an equation having the maximum degree 1.  A nonlinear equation has the degree as 2 or more than 2, but not less than 2. 
All these equations form a straight line in XY plane. These lines can be extended to any direction but in a straight form.  It forms a curve and if we increase the value of the degree, the curvature of the graph increases. 
The general representation of linear equation is;
y = mx +c Where x and y are the variables, m is the slope of the line and c is a constant value. 
The general representation of nonlinear equations is;
ax^{2} + by^{2} = c Where x and y are the variables and a,b and c are the constant values 
Examples:

Examples:

Note:
The linear equation has only one variable usually and if any equation has two variables in it, then the equation is defined as a Linear equation in two variables. For example, 5x + 2 = 1 is Linear equation in one variable. But 5x + 2y = 1 is a Linear equation in two variables.
Let us see some examples based on these concepts.
Solved Examples
Example: Solve the linear equation 3x+9 = 2x + 18.
Solution: Given, 3x+9 = 2x + 18
⇒ 3x – 2x = 18 – 9
⇒ x = 9
Example: Solve the nonlinear equation x+2y = 1 and x = y.
Solution: Given, x+2y = 1
x = y
By putting the value of x in the first equation we get,
⇒ y + 2y = 1
⇒ 3y = 1
⇒ y = ⅓
∴ x = y = ⅓
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Related Links  
Difference between Rational & Irrational Numbers  Difference Between Natural and Whole numbers 
Difference Between Exponent and Power  Difference Between Line And Line Segment 
Frequently Asked Questions – FAQs
What is the key difference between nonlinear and linear equations?
How does the graph of linear and nonlinear equations look?
How is the linear equation represented? Give an example.
where m = slope of the line
x and y are the variables
c is the intercept (constant value)
Example: 2x+y=1
y=2x+1
How is the nonlinear equation formed?
where x and y are variables
a,b and c are constant values.
good explanation of difference between Linear and Nonlinear Equations