• Angles on a straight line = $180^{\circ}$
• Vertically opposite angles are identical
• A set of parallel lines have alternate and corresponding angles
• Rotational symmetry: A shape has rotational symmetry if it still looks the same after a rotation of less than one turn ($360^{\circ}$)

Triangles

• Equilateral triangle: three sides of the same length, each angle is $60^{\circ}$
• Isosceles triangle: two equal sides, two equal angles
• Scalene triangle: different sides, different angles
• Right angle triangle: one angle is $90^{\circ}$, hypotenuse is the longest side
• The sum of angles in a triangle = $180^{\circ}$
• The size of an exterior angle can of a triangle can be found by summing the two angles opposite to it
• The sum of all exterior angles of a triangle = $360^{\circ}$

Quadrilaterals

• Any 2D shape with four straight edges, four vertices
• You can split any quadrilateral into two triangles
• Sum of interior angles = $360^{\circ}$
• Sum of exterior angles = $360^{\circ}$
• A parallelogram has two sets of parallel sides
• A trapezium has one set of parallel sides, no symmetry
• Lines are perpendicular if they intersect at a right angle. See perpendicular bisection