2D Shapes and Their Properties

What Are 2D Shapes?

2D shapes (two-dimensional shapes) are flat figures that have length and width but no depth. They are defined by their sides, angles, and symmetry.

Common 2D Shapes and Their Properties

Triangles

A triangle is defined as a shape with three sides (and by default 3 angles). In a triangle all three angles add to $180 \degree$. There are 4 main types of triangle, these are:

• Equilateral Triangle: All sides and angles are equal.
• Isosceles Triangle: Two sides and two angles are equal.
• Scalene Triangle: No equal sides or angles.
• Right-Angled Triangle: Contains a $90\degree$ angle.

 

Quadrilaterals

Quadrilaterals are shapes that have 4 sides and angles add to $360 \degree$. Here are some examples of quadrilaterals.

• Square: Four equal sides and four right angles.
• Rectangle: Opposite sides are equal; all angles are 90°.
• Parallelogram: Opposite sides and angles are equal.
• Rhombus: All sides are equal; opposite angles are equal.
• Trapezium: One pair of parallel sides.
• Kite: Two pairs of equal adjacent sides.

 

 

 

Other 2D Shapes

• Pentagon: Five sides.
• Hexagon: Six sides.
• Heptagon: Seven sides.
• Octagon: Eight sides.
• Nonagon: Nine sides
• Decagon: Ten sides

 

 

 

Circles

Circle terms you need to know and recognise

• Diameter: A line that goes from one side of the edge to the other and passes through the center. Is also a line of symmetry for the circle
• Radius: A line from the center of the circle to the circle edge. 
  • Radius is half the diameter $\text{diameter} =  2 \times \text{radius}$
• Circumference: The perimeter of a circle, i.e the circle edge
• Sector: The area formed from two radii and an arc
• Arc: A section of the circumference of a circle
• Chord: A line between two points on the circumference. It doesn't go through the center
• Segment: The area created by a chord and the circumference
• Tangent: A straight line that touches the circumference of a circle at a single point only
• Pi $(\pi)$: The ratio between the circumference and the diameter
  • i.e $\pi = \frac{circumference}{diameter}$