Polygons
Polygon A closed plane figure formed by 3 or more segments. Each segment intersects exactly 2 other segments at their endpoints. No 2 segments with a common endpoint are collinear. Note: Each segment is called a side. Each endpoint is called a vertex. To name a polygon, you start at one vertex and list the vertices in either clockwise or counterclockwise order. DO NOT SKIP AROUND! The number of letters in the name also tells you how many sides the polygon has.
Equilateral Polygon A polygon with all sides congruent. Note: on a sketch, you must put tick marks or side lengths to show all sides are congruent.
Equiangular Polygon : A polygon with all angles congruent. Note: on a sketch, you must put tick marks or angle measures to show all angles are congruent.
Regular Polygon A polygon that is both equilateral and equiangular Note: On a sketch you must put tick marks or side lengths on all the sides to show sides are congruent AND put tick marks or angle measures for the angles to show all angles are congruent.
Diagonal A segment that connects two non-consecutive vertices.
Convex Polygon A polygon that has no diagonal with points outside the polygon.
Concave Polygon A polygon that has at least one diagonal with points outside the polygon. Note: The whole diagonal does not have to be outside of the polygon. It could be all or it could be part of it.
Common Polygons Classifications # Sides Classification 3 Triangle 4 Quadrilateral 5 Pentagon 6 Hexagon 7 Heptagon 8 Octagon 9 Nonagon 10 Decagon 11 Undecagon 12 Dodecagon n N-gon
Triangles
Scalene Triangle A triangle that has no congruent sides. Note: When sketching a scalene triangle, be sure to use numbers to indicate that the sides are different lengths. (not tick marks).
Isosceles Triangle A triangle that has at least two congruent sides. Note: The two congruent sides are called legs the third side is called the base. The vertex angle is where the two legs intersect. The other two angles are called the base angles. They will always be across from the congruent sides. Be sure to include tick marks or measures of the sides to show which sides are congruent.
Equilateral Triangle A triangle whose sides are all congruent. Note: on a sketch, be sure to show tick marks or lengths of sides.
Acute Triangle A triangle that has three acute angles. Note: On a sketch, be sure to either make all angles look obviously less than 90 or write in angle measures that are all less than 90 and the three add up to 180.
Right Triangle A triangle with one right angle. Note: On a sketch, be sure to either include the 90 mark or write in 90.
Obtuse Triangle A triangle with one obtuse angle. Note: On a sketch, be sure to either make the obtuse angle look obviously greater than 90 or write in angle measure that is greater than 90 but less than 180
Quadrilaterals
Parallelogram A quadrilateral with two pairs of parallel sides. Note: On a sketch, be sure to ONLY show the sides are parallel with each other. Do not put extra marks on the sketch.
Rectangle An equiangular quadrilateral. Note: On a sketch, be sure to ONLY show the angles are all congruent with either the 90 mark, 90 written for each angle or tick marks on the angles. Do not put extra marks on the sketch.
Rhombus An equilateral quadrilateral. Note: On a sketch, be sure to ONLY show the sides are congruent with either tick marks on the sides or measures for the side lengths. Do not put extra marks on the sketch.
Square A regular quadrilateral. Note: On a sketch, be sure to show the sides are all congruent with either tick marks on the sides or measures for the side lengths AND show the angles are all congruent with either the 90 mark, 90 written for each angle or tick marks on the angles. Do not put extra marks on the sketch.
Kite A quadrilateral with two pairs of consecutive sides that are congruent and no opposite sides congruent. Note: On a sketch, be sure to ONLY show the sides are congruent with either tick marks on the sides or measures for the side lengths. Do not put extra marks on the sketch.
Trapezoid A quadrilateral with exactly one pair of parallel sides. Note: On a sketch, be sure to ONLY show the sides are parallel with each other. Do not put extra marks on the sketch.
Special Segments in Triangles
Median (in a triangle) A segment that has its endpoints on a vertex of the triangle and the midpoint of the opposite side. Note: You must put tick marks on both sides of the midpoint so show that it is a midpoint.
Angle Bisector (in a triangle) A segment from a vertex to the opposite side that separates the angle into two congruent angles. Note: Be sure to include congruency tick marks on the sketch to indicate the angles are congruent.
Altitude (in a triangle) The perpendicular segment from a vertex of the triangle to the line containing the opposite side. Note: Be sure to include the 90 mark to show the segment is perpendicular.