Geometric
Geometric
Geometric
Example 2
Find the sum of the first 20 terms of the geometric sequence:
2, 6, 18, 54 …
,
and
![GeometricEx2-4 GeometricEx2-4](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-4.png)
![GeometricEx2-5 GeometricEx2-5](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-5.png)
![GeometricEx2-6 GeometricEx2-6](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-6.png)
2, 6, 18, 54 …
Step 1. Determine a1, r and n.
![GeometricEx2-1 GeometricEx2-1](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-1.png)
![GeometricEx2-2 GeometricEx2-2](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-2.png)
![GeometricEx2-3 GeometricEx2-3](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-3.png)
Step 2. To find the series, substitute and solve.
![GeometricEx2-4 GeometricEx2-4](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-4.png)
![GeometricEx2-5 GeometricEx2-5](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-5.png)
![GeometricEx2-6 GeometricEx2-6](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-6.png)
![GeometricEx2-7 GeometricEx2-7](https://claregladwinresd.glk12.org/pluginfile.php/1012/mod_book/chapter/606/Sequence_and_Series/Images/GeometricEx2-7.png)