Chapter 2: Getting Started

@laurocaetano, @rmascarenhas, @andrielfn and @rcillo After a lot of effort on this chapter I tried my best to solve exercises and problems, but couldn't finish all of them.
yep this is wrong, it should be `n-square` since it is the summation, which gives `n(n+1)/2`

I just missed the `+` lol, this is what happens when you do it 2am