Today i had this one, hope that someone can understand & help me:

I have this math expression:

**1 + a + a^2 + a^3 + ....**(it spreads to infinite, n)

I want to re-write this via classpad (i want to apply this for exams), my teacher give us this result:

1 - a^(n+1)

1 - a

Does some classpad command do that?