Worked examples: finite geometric series | High School Math | Khan Academy

Sal evaluates three geometric series (defined in various ways) using the finite geometric series formula a(1-râ ¿)/(1-r).

High School Math on Khan Academy: Did you realize that the word "algebra" comes from Arabic (just like "algorithm" and "al jazeera" and "Aladdin")? And what is so great about algebra anyway? This tutorial doesn't explore algebra so much as it introduces the history and ideas that underpin it.

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[glutenfreebread]

the a^i=a^i-i9/10 is actually a^i=a^i-1 * 9/10 the multiplication symbol just adds on top of the 1 and makes it look like the letter "i" 4:55

[IvanLeoG]

how did you get the 100(1-(9/10)^30 from example #3? and 11( 1-(10/11)^50) from example #1?

[goldelynpelendingue]

how do you get the common ratio? because some needs to reciprocal to get the common ratio :D