The answer is 27 because 8-2=6 and 9-6=3 then 8*2=24 and 24+3=27
An alternating series

converges if

is monotonic and

as

. Here

.
Let

. Then

, which is positive for all

, so

is monotonically increasing for

. This would mean

must be a monotonically decreasing sequence over the same interval, and so must

.
Because

is monotonically increasing, but will still always be positive, it follows that

as

.
So,

converges.
= 1/2 (a + b) h let me know if this helps :)