This appendix will cover some of the math concepts used in Chapter 5, *On the Line – Rocket Through*, in a little more detail.

First, let's do a quick refresh on vectors and the way you can use Cocos2d-x to deal with them.

So what is the difference between a vector and a point? At first, they seem to be the same. Consider the following point and vector:

- Point (2, 3.5)
- Vec2 (2, 3.5)

The following figure illustrates a point and a vector:

In this figure, they each have the same value for *x* and *y*. So what's the difference?

With a vector, you always have extra information. It is as if, besides those ...

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