Polygons

polygon: a closed plane figure with 3 or more lines segments called sides; all line segments must be straight
regular polygon: a polygon with line segments that are all the same length

• triangle - three sides
• quadrilateral - four sides
• pentagon - five sides
• hexagon - six sides
• octagon - eight sides

Triangles can be classified by angle size, or line segment length.

Angles

• acute triangle: all angles are less than 90 degrees
• obtuse triangle: one angle is greater than 90 degrees
• right triangle: one angle is exactly 90 degrees

Line segment length

• equilateral triangle: all 3 sides are the same length
• isosceles triangle: has only two sides that are the same length
• scalene triangle: all sides have a different length

Quadrilaterals are four sided polygons. They can be classified into 5 different groups. Some quadrilaterals can be classified into more than one category.

• square: 4 right angles, all sides equal in length
• rectangle: 4 right angles, opposite sides are equal in length
• rhombus: 4 equal sides, opposite sides parallel
• parallelogram: opposite sides are equal in length and parallel
• trapezoid: only one pair of parallel sides