Just got finished with this question. But, this was the actual answers!
The formula for the area of a square, where the side length is the independent variable and the area is the dependent variable, is a nonlinear function, because the points of the function do not lie on a straight line. The formula for the perimeter of a square, where the side length is the independent variable and the perimeter is the dependent variable, is a linear function, because the points of the function lie on a straight line.