partial-year depreciation: straight-line, declining, and....

I am have trouble figuring out partial-year depreciation:

straight-line method
declining method
sum-of-years method

I have no problem with the depreciation is full year. Can anyone help?

Thank you!

It would help if you posted the full text of the exercise(s) on which you're working, along with the formulas you're using (with all variables defined) and a clear listing of everything you've tried so far.

Thank you.

Eliz.

straight line is pretty obvious. It's linear.

declining balance needs a better definition.

sum of years is pretty obvious. Add up the years.

Having said that, please provide the ENTIRE text and any appropriate background.