..For the equation : I have split up the particular solution into two parts, so that I have

and Mr F says: It's . I realise you've got it almost correct down below, but it's still careless here.

which gives me

Mr F says: This is wrong. Show all your working on how you got it (when you do this you will probably realise for yourself why it's wrong).

and Mr F says: Wrong. Show your working.

The solution of the corresponding homogeneous equation is of course . So for my answer I get

Where did I go wrong?