Appendix A
Geometry and Trigonometry
A.1 Triangles
Two triangles that share the same three interior angles are said to be similar (Figure A.1). The three ratios of corresponding sides for similar triangles are all equal. That is, letting 
denote the length of the edge from vertex 
to vertex 
, the following ratios are equal:
A line segment passing through a vertex and perpendicular to the opposite side of a triangle is called an altitude (Figure A.2). There are three altitudes in a triangle and they all intersect in a single point called the orthocenter. Any side of the triangle can be considered the base and the area of the triangle is one-half of the length of the base (
) times the length of the altitude (
) that is perpendicular to the base
Figure A.1 Similar triangles
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