1. Session 16 – Angles and 2D shapes

2. Types of angle and properties  Angles round the circle, acute, right, obtuse, reflex  Angles at a point = total 360  Complementary angles = total 90  Supplementary angles = total 180  Vertically Opposite angles = equal the opposite.

3. Parallel lines  Parallel lines are shown with arrows  Where another line crosses both parallels, the set of angles created will be identical  (mark on any you can easily work out, to help find the ones you need)  Corresponding  Alternate  Allied

4. Naming convention  Lowercase letter in the angle.  Angle ABC, is the angle created at point B by the lines AB and BC.  The middle letter in an angle name is always the where the angle is  Ex 23.1 - 10 minutes 1,2,3

5. Triangles  Interior angles add to 180  Acute, obtuse and right angle (name after the type of the largest interior angle)  Scalene = different sides, different angles  Isocolese = two equal sides, 2 equal angles  Equilateral = 3 equal sides, 3 equal angles (60)

6. Exterior angles  Extend one side to create the exterior angle. Interior + exterior = 180(supplementary)  Ex 23.2 Q3 and 4, Extensions 2, 5 and 6

7. Quadrilaterals  4 sides shape, 4 angles  Interior angles add up to 360  Numerals used to show sides that are the same length  Exercise 23.3 Q 5  Consider the different angle properties, try different ones until you find something that helps.

8. Polygons  Many sided shapes  Pentagon – 5 sides  Hexagon – 6 sides  Heptagon – 7 sides  Octagon – 8 sides  Remember, interior + exterior angles add up to 180

9.  The exterior angles of a polygon will add up to 360  To work out the total interior angles, split the shape into triangles. Each has 180, so it’s the number of triangles x 180  Ex 23.4

10. Regular Polygons  Regular polygons have equal length sides and all the angles are equal.  The size of all exterior angles added together is 360, so one exterior angle is 360 divided by the number of sides. Divide 360 by the exterior angle to find the number of sides  Tessellation, regular tessellation  Ex 23.5 Q 1, 4 and 5

11. Symmetry  Lines of symmetry  Order of rotational symmetry

12. Tessellation  All the angle at a point have to add up to 360.  If the do not then the shapes will not tessellate.  You may need to work out the interior angles of the given shapes and see if the add up to 360 at the points where they join.

13. Homework  Create revision notes (p 240)  Use BKSB to revise Complete the homework exam question.