Plane and solid geometry . The points of intersection of the lines are the vertices ofthe polygon, and the segments of the boundary lines includedbetween adjacent vertices are the sides of the polygon. 85. Def. The sum of the sides of a polygon is its perimeter. 86. Def. Any angle formed by two consecutive sides andfound on the right in passing clockwise around the perimeterof a polygon is called an interior angle of the polygon, or,for brevity, an angle ofthe polygon. In Tig. 1,A ABC, BCD, CDE, DEA,and EAB are interiorangles of the polygon. 87. Def. If any sideof a polygon is prolongedthrough
Plane and solid geometry . The points of intersection of the lines are the vertices ofthe polygon, and the segments of the boundary lines includedbetween adjacent vertices are the sides of the polygon. 85. Def. The sum of the sides of a polygon is its perimeter. 86. Def. Any angle formed by two consecutive sides andfound on the right in passing clockwise around the perimeterof a polygon is called an interior angle of the polygon, or,for brevity, an angle ofthe polygon. In Tig. 1,A ABC, BCD, CDE, DEA,and EAB are interiorangles of the polygon. 87. Def. If any sideof a polygon is prolongedthrough a vertex, the angleformed by the prolonga-tion and the adjacent side is called an exterior angle of thepolygon. In Fig. 1, A 1, 2, 3, 4, and 5 are exterior angles. 88. Def. A line joining any two non-adjacent vertices of apolygon is called a diagonal; as AC, Fig. 1. 89. Def. A polygon which has all of its sides equal is anequilateral polygon. 90. Def. A polygon which has all of its angles equal is ansquiangular polygon. ,. BOOK I 23 91. Def. A polygon which is both equilateral and equi-angular is a regular polygon. 92. Def. A polygon of three sides is called a triangle; oneof four sides, a quadrilateral; one of live sides, a pentagon; oneof six sides, a hexagon; and so on. TRIANGLES CLASSIFIED WITH RESPECT TO SIDES 93. Def. A triangle having no two sides equal is a scalenetriangle. 94. Def. A triangle having two sides equal is an isoscelestriangle. The equal sides are spoken of as the sides * of thetriangle. The angle between the equal sides is the vertexangle, and the side opposite the vertex angle is called the base. 95. Def. A triangle having its three sides equal is anequilateral trisuigle.
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