Hi!

1.I have no idea how to solve this integral:

http://img59.imageshack.us/img59/9750/que1hi6.gif

2.I've got two solutions from different sources to this DE, what is the difference and why they chose to write the solutions like that (how do I know when to write them as a product or as a sum)?

the equations is:

y''''+y=0

one solutions is:

http://img59.imageshack.us/img59/6232/tap1tv7.jpg

and the other:

http://img113.imageshack.us/img113/7651/tap2ro4.jpg

Thanks! :)