Is the function Linear or Nonlinear?

Is the following equation linear or nonlinear? 

Is the following equation linear or nonlinear? 

Is the following equation linear or nonlinear? 

y = 9x + 2

9x + 2y = 19

$$y\ =\ \frac{x}{12}+10$$

y = $$\sqrt[]{2x\ -\ 8}$$

y = 12x² -8x