∑_(r=1)^n▒2/r(r+1)(r+2)

∑_(r=1)^n▒r/((2r-1)(2r+1)(2r+3))

I first convert both to partial fraction.

Then i use the method of differences to cancel off term by term, but i don't what term should i cancel.

Guide me through these two questions, please. Thank you.