If the graph of a function y=f(x) is a straight line then the function is called linear function
if the graph of a function y=f(x) is not a straight line then the function is called non-linear function
Any equation in the form,
In linear function the heighest power of variable x is always 1
Whereas, in nonlinear function the heighest power of variable x is always greater than 1
example,
In the above function, the heighest power of x is 2.
hence, it is a nonlinear function