Answer
Nonlinear.
Work Step by Step
To the left of the equal sign, there is a $tan(y)$. There cannot be a function of $y$ in the equation, except a derivative of $y$ by itself. Therefore, the equation doesn't fit the form $a_o(x)y^{(n)}+a_1(x)y^{(n-1)}+...+a_n(x)y=F(x)$ and the equation must be nonlinear.
