13-5

Alright this week I’m going to talk about section 13-5. It’s all about infinite sums.

First things first, let’s see those notes!
• You can only find the infinite sum of a geometric series, it will not work for an arithmetic series
• You can only find the infinite sum of a geometric series if r < 1
• The formula for finding the infinite sum of a geometric series is as follows:
S= ((t1) / (1-r))
• To find where an infinite geometric converges, set r < 1 and solve for x
• Another thing that you need to know about this section is how to write a repeating decimal as a fraction. To do this follow this formula: (what’s repeating / place-1)

Alright how about an example?

Find the sum of the infinite geometric series.
9-6+4-…
First find r. -6/9= -2/3, 4/-6= -2/3
Next plug into the formula
S= 9 (first term)/1- (-2/3) (that’s r)
S= 9/ 5/3= 27/5

That’s all there is to it guys.
--Sarah