CHAPTER13 Triangles ......................................................................................
In This Chapter
- Classifying triangles by
sides and angles - How to find missing angles
and measure exterior
angles - The Pythagorean theorem
and how to use it - How to find area and
perimeter of triangles
Geometry is a branch of mathematics that looks at shapes.
That’s true, but “shapes” covers so much ground that the
statement really doesn’t tell you much. To understand what
geometry really looks at, what kinds of questions it tries to
answer, you need to break that down a bit.
The first big distinction you can make is that geometry looks
at shapes with straight sides, called polygons, and shapes that
curve, or circles. There are some things you can say about
all polygons, but the conversation gets more interesting when
you start to break that group down even more according to
the number of sides the polygon has.
In this chapter, we’ll explore triangles, polygons with three
sides. We’ll look at some things that are true about all
triangles, and then organize triangles into groups, based on
facts about their sides or about their angles, or both. There
will be lots to learn about right triangles, the most interesting
group. We’ll also have a look at the very practical matters of
area and perimeter.