Which function is nonlinear?

Algebraically, linear functions are polynomials with highest exponent equal to 1 or of the form y = c where c is constant. Nonlinear functions are all other functions. An example of a nonlinear function is y = x^2. This is nonlinear because, although it is a polynomial, its highest exponent is 2, not 1.

Ok but uh what do you need with?