Geometrical reasoning

Year 7
Year 8
Year 9
Year 10
Year 11
Extension
Use correctly the vocabulary, notation and labelling conventions for lines, angles and shapes.   Distinguish between conventions, definitions and derived properties. Distinguish between practical demonstration and proof in a geometrical context. Show step-by-step deduction in solving more complex geometrical problems. Understand the necessary and sufficient conditions under which generalisations, inferences and solutions to geometrical problems remain valid.
Identify parallel and perpendicular lines; know the sum of angles at a point, on a straight line and in a triangle; recognise vertically opposite angles. Identify alternate angles and corresponding angles; understand a proof that: the angle sum of a triangle is 180°and of a quadrilateral is 360° the exterior angle of a triangle is equal to the sum of the two interior opposite angles. Explain how to find, calculate and use:
• the sums of the interior and exterior angles of quadrilaterals, pentagons and hexagons
• the interior and exterior angles of regular polygons.

Inscribed regular polygons

Tessellation interactivity

Tessellations with LOGO

Generalising about Polygons LOGO

Know the definition of a circle and the names of its parts; explain why inscribed regular polygons can be constructed by equal divisions of a circle. Know that the tangent at any point on a circle is perpendicular to the radius at that point; explain why the perpendicular from the centre to the chord bisects the chord. Prove and use the facts that:
• the angle subtended by an arc at the centre of a circle is twice the angle subtended at any point on the circumference
• the angle subtended at the circumference by a semicircle is a right angle
• angles in the same segment are equal
• opposite angles in a cyclic quadrilateral sum to 180°.

Circle theorems with GSP

Prove and use the alternate segment theorem.
Identify and use angle, side and symmetry properties of triangles and quadrilaterals; explore geometrical problems involving these properties, explaining reasoning orally, using step-by-step deduction supported by diagrams. Solve geometrical problems using side and angle properties of equilateral, isosceles and right-angled triangles and special quadrilaterals, explaining reasoning with diagrams and text; classify quadrilaterals by their geometrical properties.

Quadrilaterals with 7 circles Geogebra

Transformations and tessellations DGS

Solve problems using properties of angles, of parallel and intersecting lines, and of triangles and other polygons, justifying inferences and explaining reasoning with diagrams and text. Solve multi-step problems using properties of angles, of parallel lines, and of triangles and other polygons, justifying inferences and explaining reasoning with diagrams and text.    
Know that if two 2-D shapes are congruent, corresponding sides and angles are equal. Understand congruence and explore similarity. Know that if two 2-D shapes are similar, corresponding angles are equal and corresponding sides are in the same ratio; understand from this that any two circles and any two squares are mathematically similar while in general any two rectangles are not.   Prove the congruence of triangles and verify standard ruler and compass constructions using formal arguments.
Investigate Pythagoras’ theorem, using a variety of media, through its historical and cultural roots, including ‘picture’ proofs.

Proof of Pythagoras

Discovering Pythagoras theorem using GSP

Use 2-D representations to visualise 3-D shapes and deduce some of their properties. Visualise 3-D shapes from their nets; use geometric properties of cuboids and shapes made from cuboids; use simple plans and elevations.

Building Houses

3D object viewer

Polyhedron calendars

Visualise and use 2-D representations of 3-D objects; analyse 3-D shapes through 2-D projections, including plans and elevations. Understand and apply Pythagoras' theorem when solving problems in 2-D and simple problems in 3-D. Understand and use Pythagoras' theorem to solve 3-D problems.
    Understand and use trigonometric relationships in right-angled triangles, and use these to solve problems, including those involving bearings. Use trigonometric relationships in
right-angled triangles to solve 3-D problems, including finding the angles between a line and a plane.
Draw, sketch and describe the graphs of trigonometric functions for angles of any size, including transformations involving scalings in either or both of the x and y directions.
Use the sine and cosine rules to solve 2-D and 3-D problems.
          Calculate the area of a triangle using the formula ½absinC.