$2\mathrm{.}1$ Determine whether or not the following equations are linear or nonlinear, and state the reason for your answer.

a$.y{y}^{}5y^{}y=0$

b$.y^{}siny=0$

c$.y^{}\sqrt[\phantom{2}]{y}=0$

d$.y^{}5t^2{y}^{}3y=0$

e$.,y^{}3t^{2}siny=0$

f$.y^{}{e}^{t}y=0$