## Anatomy of a Triangle

Trigonometry, as I've said, is based on the relationships of the sides of a triangle to its angles. Before we get into the heart of trigonometry, let's refresh your memory on the basics of triangles and how they fit into the coordinate system.

Triangles are made up of three line segments joined in three places. Each of
these joints is called a *vertex*. In a triangle there are three angles,
one at each vertex. These three angles must always total 180°. As you may
remember from geometry class, there are descriptive names associated with
certain types of triangles, such as *isosceles, acute, oblique, *and
*right*. We are only going to concern ourselves with one of these, the
right triangle.

A right triangle is any triangle that has a 90° angle. The right
triangle is a very useful tool for us, because two of its sides fit nicely into
the Cartesian system we use in Flash—one of them is along the *x*-axis
and another is along the *y*-axis. (No other type of triangle can claim
this!) Because of this, it is generally easier to gain information about the
length of its sides. The side of the triangle that is opposite the 90°
angle has a special name, the *hypotenuse*.