Find the general solution of $\displaystyle x^2y''-5xy'+9y=0$. Hint: Once known a solution $\displaystyle y_1(x)$, another solution is given by $\displaystyle y(x)=v(x)y_1(x)$, with $\displaystyle v(x)$ to determinate.

Attempt: I just don't know what method to use. I don't think variation of parameters work here since it's non linear.