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# Prove properties of a function satisfying xy′ – y = x sin x

Define a function for , and . Define a second function Prove that the function satisfies the differential equation Further, find all solutions to this differential equation on the interval. Prove that there is no solution such that the initial condition is satisfied. Why does this not contradict Theorem 8.3?

Proof. To prove that satisfies the given differential equation we use Theorem 8.3 to find a formula for all solutions to this differential equation. For we have, Therefore, using Theorem 8.3 we let giving us Therefore, Hence, is a solution satisfying . Also, since and are both 0 when , is valid on the entire interval .

Finally, the differential equation has no solution satisfying (since for all ). This does not contradict Theorem 8.3 since is not continuous on any interval around 1. tom says:

How about f(1)=b=C-(-T(1)) then since C must be 0, b=T(1).

2. Bro, I didn’t get the conclusion of ur demonstration:
U arrived that , how can we conclude that is a solution for ??

• Cuz in my mind, if we got and is a solution for this, we need that then , am I wrong ?

• RoRi says:

Yeah, I think you’re right. We need . I’ll try to fix it soon, but I want to think about it for a bit first in case I had some reason for thinking this was right that I don’t remember right now.

• Another thing that I guess that you should do is to separate the differencial equation in two parts, one of then in the interval and the other , it because isn’t continuous between , after this u should show that the lateral limits of were equal, showing the differenciability of .

• RoRi says:

Yeah, I’ll need to look at it and fix the whole thing. My finals are starting in less than a week though, so I probably won’t be fixing anything until after those are over. Been committing so much time to the blog, that I’m behind on my actual classes! Thanks for pointing out the problems though, please keep commenting if you find mistakes in other problems (which, no doubt, you will).