IDNLearn.com: Where curiosity meets clarity and questions find their answers. Discover the information you need from our experienced professionals who provide accurate and reliable answers to all your questions.

Which of the following geometric series converges?

Which Of The Following Geometric Series Converges class=

Sagot :

All three series converge, so the answer is D.
The common ratios for each sequence are (I) -1/9, (II) -1/10, and (III) -1/3.
Consider a geometric sequence with the first term a and common ratio |r| < 1. Then the n-th partial sum (the sum of the first n terms) of the sequence is

Multiply both sides by r :

Subtract the latter sum from the first, which eliminates all but the first and last terms:

Solve for :

Then as gets arbitrarily large, the term will converge to 0, leaving us with

So the given series converge to
(I) -243/(1 + 1/9) = -2187/10
(II) -1.1/(1 + 1/10) = -1
(III) 27/(1 + 1/3) = 18