Two-Dimensional Shapes

Two-dimensional Shapes have dimensions in only 2 directions - a width and a length.

Plane Shapes - Same as 2-dimensional shapes; The word plane means flat because these shapes are on flat surfaces

Polygons - 2D shapes with straight sides e.g. triangle, rectangle

Regular Polygons - Polygons with all sides of equal length e.g. equilateral triangle and square


Types of Polygons

NUMBER OF SIDESNAME OF POLYGON
3triangle
4quadrilateral
5pentagon
6hexagon
7heptagon
8octagon
9nonagon
10decagon
11undecagon
un- = 1
deca- = 10
12dodecagon
do- = 2
deca- = 10

Did You Know That...?

Most names for 2D shapes and 3D solids come from the Greek language.

Many 2D shapes have names ending in -gon. Many 3D solids have names ending in -hedron.

Hept- is Greek for "seven". Sept- is Latin for "seven".

Types of Triangles

DIAGRAMNAME OF TRIANGLEPROPERTIES
Diagram of right-angled triangleRight-angled triangleHas one angle of 90°
Longest side is called the hypotenuse
Diagram of  equilateral triangleEquilateral triangle3 sides are equal
3 angles are equal
Each angle is 60°
Diagram of isosceles triangleIsosceles triangle2 sides are equal
2 angles are equal
Diagram of scalene triangleScalene triangleNo sides are equal
No angles are equal


Types of Quadrilaterals

PARALLELOGRAM
Diagram of a parallelogram
  • Opposite sides parallel
  • Opposite sides equal
  • Opposite angles equal
  • Diagonals bisect each other
RHOMBUS
Diagram of a rhombus
  • Opposite sides parallel
  • Opposite sides equal
  • Opposite angles equal
  • All sides equal
  • Diagonals equal
  • Diagonals bisect each other
  • Diagonals meet at right angles
  • Diagonals bisect the angles at the vertices (corners)
RECTANGLE
Diagram of a rectangle
  • Opposite sides parallel
  • Opposite sides equal
  • Opposite angles equal
  • All sides equal
  • Diagonals equal
  • Diagonals bisect each other
SQUARE
Diagram of a square
  • Opposite sides parallel
  • Opposite sides equal
  • Opposite angles equal
  • All sides equal
  • All angles equal
  • Diagonals equal
  • Diagonals bisect each other
  • Diagonals meet at right angles
  • Diagonals bisect the angles at the vertices (corners)
TRAPEZOID
Diagram of a trapezoid
  • Opposite sides parallel (one pair only)
  • Diagonals bisect each other
KITE
Diagram of a kite
  • 2 pairs of sides equal but not opposite sides equal
  • 1 pair of opposite angles equal
  • 1 diagonal bisects the other diagonal
  • Diagonals meet at right angles
  • 1 diagonal bisects one pair of angles

Questions - What am I?

Q1. I have 3 sides of equal length.

Q2. I have 4 equal sides, my diagonals bisect each other and the angles, and none of my angles are right angles.

Q3. I have 2 pairs of equal sides, my diagonals are not equal, my diagonals meet each other at right angles, and one pair of my opposite angles is equal.

Answers
A1. equilateral triangle
A2. rhombus
A3. kite