How do I determine if this equation is a linear function or a nonlinear function? Solution The easiest way I have for knowing the difference between linear and nonlinear is the exponent value on the variable x. It is important to understand the root word in linear. It is LINE. A straight line, no curves. For example: y = 2x - 3 This is linear because the exponent on x is one. Thus your slope is standard rise over run, like a stair step and simply goes up or down. Y = x^2 + x + 4 is nonlinear. When graphed it becomes a parabola, which looks like a hill on your graph. This is because the exponent on the variable of x is more than one. This pattern continues on for all equations. Hope this helps to put it into easy to understand terms. :).