Three equilateral triangles ABC, AYX and XZB are drawn with the point X a moveable point on AB. The points P, Q and R are the centres of the three triangles. What can you say about triangle PQR?
Can you use the diagram to prove the AM-GM inequality?
Can you discover whether this is a fair game?
The picture illustrates the sum 1 + 2 + 3 + 4 = (4 x 5)/2. Prove the general formula for the sum of the first n natural numbers and the formula for the sum of the cubes of the first n natural. . . .
Can you see how this picture illustrates the formula for the sum of the first six cube numbers?
Imagine two identical cylindrical pipes meeting at right angles and think about the shape of the space which belongs to both pipes. Early Chinese mathematicians call this shape the mouhefanggai.
Prove Pythagoras' Theorem using enlargements and scale factors.
A circle has centre O and angle POR = angle QOR. Construct tangents at P and Q meeting at T. Draw a circle with diameter OT. Do P and Q lie inside, or on, or outside this circle?
We are given a regular icosahedron having three red vertices. Show that it has a vertex that has at least two red neighbours.
Pick a square within a multiplication square and add the numbers on each diagonal. What do you notice?
Four jewellers share their stock. Can you work out the relative values of their gems?
Do you have enough information to work out the area of the shaded quadrilateral?
What can you say about the lengths of the sides of a quadrilateral whose vertices are on a unit circle?
The first of two articles on Pythagorean Triples which asks how many right angled triangles can you find with the lengths of each side exactly a whole number measurement. Try it!
Is the mean of the squares of two numbers greater than, or less than, the square of their means?
This is the second article on right-angled triangles whose edge lengths are whole numbers.
Three points A, B and C lie in this order on a line, and P is any point in the plane. Use the Cosine Rule to prove the following statement.
Some puzzles requiring no knowledge of knot theory, just a careful inspection of the patterns. A glimpse of the classification of knots and a little about prime knots, crossing numbers and. . . .
This article discusses how every Pythagorean triple (a, b, c) can be illustrated by a square and an L shape within another square. You are invited to find some triples for yourself.
Patterns that repeat in a line are strangely interesting. How many types are there and how do you tell one type from another?
Keep constructing triangles in the incircle of the previous triangle. What happens?
Toni Beardon has chosen this article introducing a rich area for practical exploration and discovery in 3D geometry
The largest square which fits into a circle is ABCD and EFGH is a square with G and H on the line CD and E and F on the circumference of the circle. Show that AB = 5EF. Similarly the largest. . . .
What is the largest number of intersection points that a triangle and a quadrilateral can have?
Kyle and his teacher disagree about his test score - who is right?
What fractions can you divide the diagonal of a square into by simple folding?
When is it impossible to make number sandwiches?
Can you make sense of the three methods to work out the area of the kite in the square?
Construct two equilateral triangles on a straight line. There are two lengths that look the same - can you prove it?
L triominoes can fit together to make larger versions of themselves. Is every size possible to make in this way?
Explore what happens when you draw graphs of quadratic equations with coefficients based on a geometric sequence.
Draw some quadrilaterals on a 9-point circle and work out the angles. Is there a theorem?
Can you make sense of these three proofs of Pythagoras' Theorem?
Can you work through these direct proofs, using our interactive proof sorters?
Investigate the number of points with integer coordinates on circles with centres at the origin for which the square of the radius is a power of 5.
This shape comprises four semi-circles. What is the relationship between the area of the shaded region and the area of the circle on AB as diameter?
This article invites you to get familiar with a strategic game called "sprouts". The game is simple enough for younger children to understand, and has also provided experienced mathematicians with. . . .
It is obvious that we can fit four circles of diameter 1 unit in a square of side 2 without overlapping. What is the smallest square into which we can fit 3 circles of diameter 1 unit?
Prove that, given any three parallel lines, an equilateral triangle always exists with one vertex on each of the three lines.
Semicircles are drawn on the sides of a rectangle. Prove that the sum of the areas of the four crescents is equal to the area of the rectangle.
Prove that the shaded area of the semicircle is equal to the area of the inner circle.
Take any rectangle ABCD such that AB > BC. The point P is on AB and Q is on CD. Show that there is exactly one position of P and Q such that APCQ is a rhombus.
Janine noticed, while studying some cube numbers, that if you take three consecutive whole numbers and multiply them together and then add the middle number of the three, you get the middle number. . . .
ABCD is a square. P is the midpoint of AB and is joined to C. A line from D perpendicular to PC meets the line at the point Q. Prove AQ = AD.
It is impossible to trisect an angle using only ruler and compasses but it can be done using a carpenter's square.
Can you find the areas of the trapezia in this sequence?
Clearly if a, b and c are the lengths of the sides of an equilateral triangle then a^2 + b^2 + c^2 = ab + bc + ca. Is the converse true?
The diagonal of a square intersects the line joining one of the unused corners to the midpoint of the opposite side. What do you notice about the line segments produced?
Mark a point P inside a closed curve. Is it always possible to find two points that lie on the curve, such that P is the mid point of the line joining these two points?
A picture is made by joining five small quadrilaterals together to make a large quadrilateral. Is it possible to draw a similar picture if all the small quadrilaterals are cyclic?