Introduction to Geometry

• Polyhedron - a 3-D figure

  
• Polygon - a closed plane figure with at least 3 straight sides

  
• Line segment - a part of a line that has two endpoints

  
• Line - a line that continues forever in both directions

  
• Ray - a line with only one endpoint

  
• Point

  
• Parallel lines - lines that are always the same distance apart. They NEVER intersect.

  
• Angle - formed by two rays with the same endpoint

  
• Vertex - the point of intersection of rays or lines that form an angle

  
• Right angle - a 90-degree angle

  
• Perpendicular lines - two lines that form a right angle

  
• Congruent angles - the shapes, lines or angles are equal in size