Make five different quadrilaterals on a nine-point pegboard, without using the centre peg. Work out the angles in each quadrilateral you make. Now, what other relationships you can see?
Draw some angles inside a rectangle. What do you notice? Can you prove it?
An environment that enables you to investigate tessellations of regular polygons
Can you find triangles on a 9-point circle? Can you work out their angles?
What is the relationship between the angle at the centre and the angles at the circumference, for angles which stand on the same arc? Can you prove it?
Draw some quadrilaterals on a 9-point circle and work out the angles. Is there a theorem?
Never used GeoGebra before? This article for complete beginners will help you to get started with this free dynamic geometry software.
Can you make a right-angled triangle on this peg-board by joining up three points round the edge?
A dot starts at the point (1,0) and turns anticlockwise. Can you estimate the height of the dot after it has turned through 45 degrees? Can you calculate its height?
Show how this pentagonal tile can be used to tile the plane and describe the transformations which map this pentagon to its images in the tiling.
A circle rolls around the outside edge of a square so that its circumference always touches the edge of the square. Can you describe the locus of the centre of the circle?
Construct two equilateral triangles on a straight line. There are two lengths that look the same - can you prove it?
Semi-regular tessellations combine two or more different regular polygons to fill the plane. Can you find all the semi-regular tessellations?
A right-angled isosceles triangle is rotated about the centre point of a square. What can you say about the area of the part of the square covered by the triangle as it rotates?
Join pentagons together edge to edge. Will they form a ring?
Using a ruler, pencil and compasses only, it is possible to construct a square inside any triangle so that all four vertices touch the sides of the triangle.
Can you make sense of these three proofs of Pythagoras' Theorem?
If you continue the pattern, can you predict what each of the following areas will be? Try to explain your prediction.
L triominoes can fit together to make larger versions of themselves. Is every size possible to make in this way?
How good are you at estimating angles?
Medieval stonemasons used a method to construct octagons using ruler and compasses... Is the octagon regular? Proof please.
Move the point P to see how P' moves. Then use your insights to calculate a missing length.
Can you work out how to produce different shades of pink paint?
Complex numbers can be represented graphically using an Argand diagram. This problem explains more...
Can you find an efficent way to mix paints in any ratio?
Can you put the 25 coloured tiles into the 5 x 5 square so that no column, no row and no diagonal line have tiles of the same colour in them?
The opposite vertices of a square have coordinates (a,b) and (c,d). What are the coordinates of the other vertices?
Explore the area of families of parallelograms and triangles. Can you find rules to work out the areas?
The farmers want to redraw their field boundary but keep the area the same. Can you advise them?
The length AM can be calculated using trigonometry in two different ways. Create this pair of equivalent calculations for different peg boards, notice a general result, and account for it.
Can you work out the fraction of the original triangle that is covered by the inner triangle?
The sine of an angle is equal to the cosine of its complement. Can you explain why and does this rule extend beyond angles of 90 degrees?
Join the midpoints of a quadrilateral to get a new quadrilateral. What is special about it?
Cartesian Coordinates are not the only way!
Can you explain what is happening and account for the values being displayed?
How can visual patterns be used to prove sums of series?
A tool for generating random integers.
The points P, Q, R and S are the midpoints of the edges of a non-convex quadrilateral.What do you notice about the quadrilateral PQRS and its area?
What happens when we multiply a complex number by a real or an imaginary number?
What happens when we add together two complex numbers?
Let's go further and see what happens when we multiply two complex numbers together!
Can you devise a system for making sense of complex multiplication?
Take any triangle, and construct squares on each of its sides. What do you notice about the areas of the new triangles formed?
Use the applet to make some squares. What patterns do you notice in the coordinates?
Is there a relationship between the coordinates of the endpoints of a line and the number of grid squares it crosses?
Use the applet to explore the area of a parallelogram and how it relates to vectors.
Move the corner of the rectangle. Can you work out what the purple number represents?
Investigate what happens to the equations of different lines when you reflect them in one of the axes. Try to predict what will happen. Explain your findings.
P is a point on the circumference of a circle radius r which rolls, without slipping, inside a circle of radius 2r. What is the locus of P?
How well can you estimate angles? Playing this game could improve your skills.