Why do you need to reduce it?
1) Create a system z = d2y/dx2. What does that do after some substitution?
2) Factor the characteristic polynomial in ignorance ==> I didn't even notice it wasn't second degree! Just see what happens.
d4y/dx4 - 8( d2y/dx2) + 16y = 0
This is on one of my '2nd order differential equations' problem sheets and its a of fourth order leaving me a bit confused. Ive tried reducing the order but I cant get it. Is there a rule/theorem Ive missed??
A helping hand would be greatly appreciated