$\"\"$

The sum of an infinite geometric series is $\"\"$ , with $\"\"$ ,

Where $\"\"$ is first term and r is common ratio.

The infinite geometric series is $\"\"$ ,

In the series are $\"\"$ .

$\"\"$ , the sum exists. $\"\"$

$\"\"$ (Substitute $\"\"$ )

$\"\"$ (Subtract denominator: $\"\"$ )

$\"\"$ (Divide: $\"\"$ ) $\"\"$

The sum of the infinite geometric series is 20.