How to solve this ordinary differential equation $tx'''+3x''-tx'-x=0$?
For equation $tx''' +3x''-tx'-x=0$, we know a special solution $x_1=\frac{1}{t}$, how to general solution?
I firstly attempted $d(tx''+2x'-tx)=0$,then $tx'' +2x' -tx = C$,$C$ is a constant.But in next step , I found that my solution is wrong.Since $x_1=\frac{1}{t}$ is a special solution of $tx''' +3x''-tx'-x=0$,we found $x_2 = -\frac{1}{t}$ is a solution of equation.Then $x = x_1-x_2 =\frac{2}{t}$ is a solution of $tx''+2x'-tx=0$.As you can see ,the step is wrong.
Then I attemped other way to solve this equation ,but all failed.Could help me solve this equation?Thans!
We can use Reduction of Order, we have
$$tx''' +3x''-tx'-x=0, ~~~~x_1 = \dfrac{1}{t}$$
Let
$$x_2 = v~ x_1 = \dfrac{v}{t}$$
Taking derivatives, substituting and simplifying into $tx_2''' +3x_2''-tx_2'-x_2=0$
$$v''' - v' = 0$$
Let $w = v'$, so we have
$$w'' - w = 0 \implies w = a e^t + b e^{-t}$$
This gives
$$v = a e^t + b e^{-t} + c$$
From the initial substitution
$$x_2 = \dfrac{v}{t} = \dfrac{a e^t + b e^{-t} + c}{t}$$