Uh oh! Wolfram|Alpha doesn't run without JavaScript.
Please enable JavaScript. If you don't know how, you can find instructions
here
.
Once you've done that, refresh this page to start using Wolfram|Alpha.
-18 + \sum_{n = 0}^{\infty} (18 * (2/3)^n)
-18 + \sum_{n = 0}^{\infty} (18 * (2/3)^n)
Natural Language
Math Input
Extended Keyboard
