Geometry
Angles & Lines
A right angle measures 90°, an acute angle is less than 90°, and an obtuse angle is more than 90° but less than 180°.
Parallel lines always stay the same distance apart and never meet, like railway tracks. Perpendicular lines cross each other making a right angle.
- Right = 90°, acute < 90°, obtuse > 90°.
- Parallel lines never meet; perpendicular lines meet at a right angle.
Parts of a Circle
The centre is the middle of a circle. The radius is the distance from the centre to the edge. The diameter goes right across through the centre and equals two radii (diameter = 2 × radius). A chord joins any two points on the circle, and the longest chord is the diameter.
- Radius = centre to edge; diameter = across through the centre.
- Diameter = 2 × radius; the longest chord is the diameter.
Symmetry & Nets
A shape has line symmetry if a line splits it into two matching halves. A square has 4 lines of symmetry, a rectangle has 2, and a circle has many.
A net is a flat shape that folds into a solid. The net of a cube has 6 square faces, and the net of a cuboid has 6 rectangular faces.
- Square has 4 lines of symmetry; rectangle has 2.
- A net folds into a solid; a cube's net has 6 squares.