I totally understand the problem. I went through school under the impression I was useless at maths, which was rather a self fulfilling prophesy

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In my experience, there are only a few areas of maths that are really relevant for games. I'll list the main ones that I've found useful below, with a quick explanation of why you might need them. Hopefully they should all be Googlable for reasonable results.

**Vectors** (addition, subtraction, scaling, normalisation, dot product, cross product).

- These are useful for a huge range of directional and movement work, and will probably provide everything you need for your current 2D project.

**Interpolation and splines** (linear interpolation, b-splines, catmul-rom splines etc.).

- These are useful for creating smooth movement paths, among other things.

**Integration** (Euler integration, Runge-Kutta fourth order integration).

- Integration is used for modelling changes over time accurately (or inaccurately in the case of Euler integration). This can be useful for calculating speed from acceleration etc. although if you're using Box2D in AppGameKit, you shouldn't need to worry about this.

**Collision detection** (there are lots of these: separating axis theorem, bounding volumes, ray casting etc.).

- These are vital for lots of game interactions, but are often irrelevant in AppGameKit because it provides so many collision detection functions itself.

**Matrices** (matrix multiplication)

- Matrices are used for lots of stuff inside rendering engines, but are less useful in day to day gameplay programming. However they can be useful for performing local transformations, for example getting objects to rotate around a point.

**Quaternions**
- These are a clever way of representing arbitrary rotations in 3D space, and so are quite often used for things like camera angles etc.

There is plenty more out there, and I'm certainly not saying you need all this to make games! To be honest, the only one that really crops up day to day is vectors. However I hope this gives you a reasonable starting point. If you want any specific examples of these, just let me know.