Geometrical terms

A point marks a position. A line is straight and has length but no width. Parallel lines stay the same distance apart and never meet. Perpendicular lines meet at a right angle. A vertex is a corner where two lines meet.

An acute angle is less than 90°. A right angle is exactly 90°. An obtuse angle is between 90° and 180°. A reflex angle is between 180° and 360°.

In a polygon, an interior angle is inside the shape at a vertex. An exterior angle is between one side and the next side extended. A bearing is an angle measured clockwise from north.

Congruent shapes are exactly the same shape and size. Similar shapes have the same shape but not always the same size.

The scale factor is the number each length is multiplied by to get the matching length on a similar shape. You do not have to show that two shapes are congruent.

Triangles: equilateral (three equal sides), isosceles (two equal sides), scalene (no equal sides) and right-angled (one right angle).

Quadrilaterals: square, rectangle, kite, rhombus, parallelogram and trapezium. A rhombus has four equal sides and opposite angles that are equal. A parallelogram has opposite sides that are parallel and of equal length. A trapezium has one pair of parallel sides. A kite has two pairs of equal adjacent sides.

When asked for properties, give two from different aspects: sides, angles, diagonals or symmetry. A property that fits every quadrilateral, such as 4 sides, does not score.

A polygon is a closed shape with straight sides. A regular polygon has all sides equal and all angles equal. An irregular polygon does not.

Names by number of sides: pentagon 5, hexagon 6, octagon 8, decagon 10.

A net is a flat shape that folds up to make a solid. Draw every face: a net of a closed box with only five faces is an open box. A net is flat, not a 3-dimensional drawing.

Simple solids: cube, cuboid, prism, cylinder, pyramid, cone and sphere. A prism has a constant cross-section. A face is a flat surface of a solid. A surface can also be curved, as on a cylinder, cone or sphere. An edge is where two faces meet. A cuboid has six rectangular faces.

A pyramid has a flat base and triangular faces that meet at a point. A cone has a circular base and one curved surface.

The circumference is the distance round a circle. The radius (plural radii) goes from the centre to the circumference. The diameter goes through the centre from one side to the other.

A chord joins two points on the circumference. A tangent is a line that touches the circle at one point. An arc is part of the circumference. A sector is a region between two radii and an arc. A segment is a region between a chord and an arc. A semicircle is half a circle.

The diameter is twice the radius. A chord that passes through the centre is a diameter.

A plane is a flat surface that extends without end. A perpendicular bisector cuts a line in half at a right angle.

A hemisphere is half a sphere. A frustum is a cone with the top cut off by a plane parallel to the base.

A chord that is not a diameter splits the circumference into a major arc (the longer) and a minor arc (the shorter).