#separator:tab #html:false #tags column:4 Triangle 3 sides, 3 angles math-2d-shapes Quadrilateral 4 sides, 4 angles math-2d-shapes Pentagon 5 sides math-2d-shapes Hexagon 6 sides math-2d-shapes Heptagon 7 sides (Also called a septagon) math-2d-shapes Octagon 8 sides (A stop sign) math-2d-shapes Nonagon 9 sides math-2d-shapes Decagon 10 sides math-2d-shapes Hendecagon 11 sides (Also called an undecagon) math-2d-shapes Dodecagon 12 sides math-2d-shapes Circle All points the same distance from the center; no sides or corners math-2d-shapes Oval (ellipse) A stretched circle math-2d-shapes Square 4 equal sides and 4 right angles math-2d-shapes Rectangle 4 right angles; opposite sides equal math-2d-shapes Rhombus 4 equal sides; opposite angles equal math-2d-shapes Parallelogram Both pairs of opposite sides are parallel and equal math-2d-shapes Trapezoid A quadrilateral with at least one pair of parallel sides math-2d-shapes Kite A quadrilateral with two pairs of equal sides that meet side by side math-2d-shapes Equilateral triangle All 3 sides equal; all angles 60 degrees math-2d-shapes Isosceles triangle At least 2 equal sides and 2 equal angles math-2d-shapes Scalene triangle No equal sides math-2d-shapes Right triangle Has one 90-degree angle math-2d-shapes Acute triangle All three angles are less than 90 degrees math-2d-shapes Obtuse triangle Has one angle greater than 90 degrees math-2d-shapes Regular polygon A polygon with all sides equal and all angles equal math-2d-shapes Irregular polygon A polygon whose sides or angles are not all equal math-2d-shapes Convex polygon A polygon with no angle pointing inward math-2d-shapes Concave polygon A polygon with at least one angle pointing inward math-2d-shapes Sum of angles in a triangle 180 degrees math-2d-shapes Sum of angles in a quadrilateral 360 degrees math-2d-shapes Sum of angles in a pentagon 540 degrees math-2d-shapes Sum of angles in a hexagon 720 degrees math-2d-shapes Sum of angles in an n-sided polygon (n − 2) × 180 degrees math-2d-shapes Each angle of a regular hexagon 120 degrees math-2d-shapes Each angle of a regular pentagon 108 degrees math-2d-shapes Each angle of a regular octagon 135 degrees math-2d-shapes Number of diagonals of a quadrilateral 2 math-2d-shapes Number of diagonals of a pentagon 5 math-2d-shapes Number of diagonals of a hexagon 9 math-2d-shapes Diagonal A segment joining two corners of a polygon that are not next to each other math-2d-shapes Is a square a rectangle? Yes. A square is a rectangle with all sides equal. math-2d-shapes Is a square a rhombus? Yes. A square is a rhombus with right angles. math-2d-shapes Is a rectangle a parallelogram? Yes. Its opposite sides are parallel. math-2d-shapes Do the diagonals of a rectangle have equal lengths? Yes math-2d-shapes Do the diagonals of a rhombus meet at right angles? Yes, and they bisect each other math-2d-shapes Crescent A moon shape formed by two arcs math-2d-shapes Semicircle Half of a circle math-2d-shapes Quarter circle A quarter of a circle; a 90-degree sector math-2d-shapes Star shape (pentagram) A five-pointed star drawn with five straight lines math-2d-shapes