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# Flash Game Design: Trigonometry 101

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## 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.