In the following attachment file, I have trouble trying to understand a step in sum no.2. In the Step 2 category, 3rd line, I didn't understood how they simplified from the previous step.(adsbygoogle = window.adsbygoogle || []).push({});

Also, wanted to ask one basic question. What exactly is the purpose of that sum in mathematical world? I mean how can I apply this knowledge of expanding functions in practical life?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Expansion of functions

**Physics Forums | Science Articles, Homework Help, Discussion**