1. (x+a) y' -3y = (x+a)^4

2. Interchange dependent and independent variables to solve:

(2x-5y^3) y' + y = 0, y(1)=1

3. Using the subst. z=y^-2 solve:

y' = xy - y^3 e^-x^2

4. Using the subst. 1+x = e^t solve:

(1+x)^2 y" + (1+x) y' + y =4cos(ln(1+x))

Any help will be much appreciated.