**OK, this is going to blow your mind! In this section, I'm going to add up an infinite number of numbers -- all positive -- and get a FINITE answer!**

**Think about it...**

**If you add these guys... forever...**

**The answer would be infinite -- right?**

**Well, I'm going to get a number. Just wait. We'll get to it in awhile.**

**First, let's check out the sigma notation for geometric sequences:**

**Here's an example:**

**TRY IT:**

**Find the sigma notation for**

*** hint: Find r first, then get the nth term formula.**