## Points to Remember

Trigonometry is the branch of mathematics that deals with the relationships between the sides and angles of triangles.

In game programming, trigonometry is used to help determine trajectories, distances, and deflection after a collision, to name a few of its functions.

Flash uses the grid-based Cartesian coordinate system to identify, place, and move objects.

By default, the registration point of a Flash movie clip is the upper-left corner of stage or movie.

The unit of measurement that Flash uses for angles is not degrees, but radians. You can easily convert from one unit of measurement to the other to work in a more familiar manner. The one exception to having to use radians in Flash is when you're changing the _rotation property of a movie clip.

You can use the Pythagorean theorem to find the distance between two points.

The trigonometric functions sine, cosine, and tangent use various ratios of the triangle side lengths to determine values and, used inversely, to deliver results as angles.

A vector is a mathematical object that has both magnitude (a numeric value) and direction. For example, velocity is a vector because it has both magnitude and direction. Vectors can be divided up into

*x*and*y*components to project it along the axes of the coordinate system. This is called*resolving*a vector.