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Properties of 2D shapes introduces students to key vocabulary used to describe the uniqe properties of 2D and 3D shapes. This is a prerequisite unit before moving on to drawing 3D shapes in Term 2 of Year 9. Learning progresses from describing 2D shapes to performing basic transformations such as rotations, enlargements, translations and reflections.

**Prerequisite Knowledge**

- distinguish between regular and irregular polygons based on reasoning about equal sides and angles.
- know angles are measured in degrees: estimate and compare acute, obtuse and reflex angles
- draw 2-D shapes using given dimensions and angles

**Success Criteria**

- use conventional terms and notations: points, lines, vertices, edges, planes, parallel lines, perpendicular lines, right angles, polygons, regular polygons and polygons with reflection and/or rotation symmetries; use the standard conventions for labelling and referring to the sides and angles of triangles; draw diagrams from written description
- derive and apply the properties and definitions of: special types of quadrilaterals, including square, rectangle, parallelogram, trapezium, kite and rhombus; and triangles and other plane figures using appropriate language
- identify and apply circle definitions and properties, including: centre, radius, chord, diameter, circumference, tangent, arc, sector and segment

**Key Concepts**

- Understanding and using the vocabulary is key throughout this topic.
- Regular polygons are closed shapes with straight lines of equal length.
- Students need to recognise different types of quadrilaterals and triangles by their geometrical properties.
- All shapes have a rotational symmetry of at least one.
- Reflected vertices are an equal distance from the line of symmetry.

**Common Misconceptions**

- Students often confuse the part of a circle.
- Diagonal lines do not have to be slanted and can be horizontal or vertical.
- A circle is not a polygon since its edge of not straight.
- Rectangles are incorrectly assumed to have a rotational symmetry of order 4.

March 6, 2021

Fun activities to celebrate Pi Day with your mathematics class.