Help with Sums!!!

[CompletelyLost???]

I need help on the following.
Directions: Find the given sum, or explain why it does not exist. (We just started with sums and I am very confused)

a. 1 - 2/3 + 4/9 - 8/27 + ...

I also need help with this one too

b. 1/3 + Square Root 2/3 + 2/3 + 2 square root 2/3 + ...

 

[Bob Brown MSEE]

Geometric Series

Each is a Geometric Series.
1) What is the multiplier?
2) Do you know the formula that gives the sum, when you know the multiplier?

 

[CompletelyLost???]

is it the formula that goes Sn=a(1-r^n)/(1-r)

 

[CompletelyLost???]

the first problem is being multiplied by 2/3 to get to the next term

 

[Bob Brown MSEE]

Yes, excellent ... now can you calculate the sum for question#1 ?

 

[CompletelyLost???]

what would I plug into the formula?

 

[CompletelyLost???]

what would the multiplier be for the second question I am really struggling with it

 

[stapel]

what would the multiplier be for the second question I am really struggling with it

Try applying the method they taught you for determining if a series is geometric; namely, dividing pairs of successive terms, and simplifying the result.

 

[Deleted member 4993]

the first problem is being multiplied by 2/3 to get to the next term

The multiplier is (-2/3)

Watch that "negative" sign!