Thread: ratio test, i need a bit of clarification

i'm looking at this problem online, and i don't understand how they came up with the answer.
Visual Calculus - Series - 12

so when they add 1, how does (2n-1) turn into (2n+1)? wouldn't the -1 and +1 cancel out, and it'd just be 2n?

Originally Posted by isuckatcalc

i'm looking at this problem online, and i don't understand how they came up with the answer.
Visual Calculus - Series - 12

so when they add 1, how does (2n-1) turn into (2n+1)? wouldn't the -1 and +1 cancel out, and it'd just be 2n?

no, you replace n with (n + 1), so 2n - 1 ---> 2(n + 1) - 1 = 2n + 2 - 1 = 2n + 1

note that things should be in absolute values

Which problem in that exercise are you referring to?

sorry, i thought i linked directly to it. i meant the third one down the list.

thanks jhevon, that makes much more sense.