which of these equations define y as a nonlinear function of x

The values of the nonlinear function will not form a straight line when graphed, then
nonlinear function are:
[tex]\begin{gathered} y=(2x+5)^2 \\ y=\frac{9}{x}-6 \\ y=2x^3+1 \end{gathered}[/tex]answer: B, C and F