Is this diffrential equation linear or non-liner?

Question

1.) y'' + (2/x)*y' + 3 = x^3

2.) x*y^3 + x^3 *y' - 3

3.) sin(x)*y^(4) - (1/x)*y^(2) = cos(x)

4.) y'' + 2x* (y')^5 = e^4x

Answer 1

1.) Linear

2.) Non-linear, because of y³

3.) It not differential equation, because no derivatives and not linear for y and forx

4.) Non-linear because (y')⁵