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Draw three equal line segments in a unit circle to divide the circle into four parts of equal area.

Challenge Level

An observer is on top of a lighthouse. How far from the foot of the lighthouse is the horizon that the observer can see?

Challenge Level

One side of a triangle is divided into segments of length a and b by the inscribed circle, with radius r. Prove that the area is: abr(a+b)/ab-r^2

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Without using a calculator, computer or tables find the exact values of cos36cos72 and also cos36 - cos72.

Challenge Level

Describe how to construct three circles which have areas in the ratio 1:2:3.

Challenge Level

Two perpendicular lines lie across each other and the end points are joined to form a quadrilateral. Eight ratios are defined, three are given but five need to be found.

Challenge Level

Ten squares form regular rings either with adjacent or opposite vertices touching. Calculate the inner and outer radii of the rings that surround the squares.

Challenge Level

A belt of thin wire, length L, binds together two cylindrical welding rods, whose radii are R and r, by passing all the way around them both. Find L in terms of R and r.

Challenge Level

What are the shortest distances between the centres of opposite faces of a regular solid dodecahedron on the surface and through the middle of the dodecahedron?

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Follow instructions to fold sheets of A4 paper into pentagons and assemble them to form a dodecahedron. Calculate the error in the angle of the not perfectly regular pentagons you make.

Challenge Level

Two problems about infinite processes where smaller and smaller steps are taken and you have to discover what happens in the limit.

Challenge Level

The sides of a triangle are 25, 39 and 40 units of length. Find the diameter of the circumscribed circle.

Challenge Level

Two places are diametrically opposite each other on the same line of latitude. Compare the distances between them travelling along the line of latitude and travelling over the nearest pole.

Challenge Level

Find the exact values of some trig. ratios from this rectangle in which a cyclic quadrilateral cuts off four right angled triangles.

Challenge Level

Can you deduce the familiar properties of the sine and cosine functions starting from these three different mathematical representations?

Challenge Level

If a is the radius of the axle, b the radius of each ball-bearing, and c the radius of the hub, why does the number of ball bearings n determine the ratio c/a? Find a formula for c/a in terms of n.

Challenge Level

Re-arrange the pieces of the puzzle to form a rectangle and then to form an equilateral triangle. Calculate the angles and lengths.

Challenge Level

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?

Challenge Level

The area of a square inscribed in a circle with a unit radius is, satisfyingly, 2. What is the area of a regular hexagon inscribed in a circle with a unit radius?

Challenge Level

Prove that the shaded area of the semicircle is equal to the area of the inner circle.

Challenge Level

On a nine-point pegboard a band is stretched over 4 pegs in a "figure of 8" arrangement. How many different "figure of 8" arrangements can be made ?

Challenge Level

What is an AC voltage? How much power does an AC power source supply?

The third of three articles on the History of Trigonometry.

The second of three articles on the History of Trigonometry.

The first of three articles on the History of Trigonometry. This takes us from the Egyptians to early work on trigonometry in China.

Challenge Level

Join some regular octahedra, face touching face and one vertex of each meeting at a point. How many octahedra can you fit around this point?

Challenge Level

How can you represent the curvature of a cylinder on a flat piece of paper?

Challenge Level

Three squares are drawn on the sides of a triangle ABC. Their areas are respectively 18 000, 20 000 and 26 000 square centimetres. If the outer vertices of the squares are joined, three more. . . .

Challenge Level

The area of a regular pentagon looks about twice as a big as the pentangle star drawn within it. Is it?

Challenge Level

Trigonometry, circles and triangles combine in this short challenge.

Challenge Level

Straight lines are drawn from each corner of a square to the mid points of the opposite sides. Express the area of the octagon that is formed at the centre as a fraction of the area of the square.

Challenge Level

Can you prove this formula for finding the area of a quadrilateral from its diagonals?

Challenge Level

How far should the roof overhang to shade windows from the mid-day sun?

Challenge Level

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?

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Prove Pythagoras' Theorem for right-angled spherical triangles.

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Which is larger cos(sin x) or sin(cos x) ? Does this depend on x ?

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The Earth is further from the Sun than Venus, but how much further? Twice as far? Ten times?

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From the measurements and the clue given find the area of the square that is not covered by the triangle and the circle.

Challenge Level

Six circular discs are packed in different-shaped boxes so that the discs touch their neighbours and the sides of the box. Can you put the boxes in order according to the areas of their bases?

Challenge Level

How would you design the tiering of seats in a stadium so that all spectators have a good view?

Logo helps us to understand gradients of lines and why Muggles Magic is not magic but mathematics. See the problem Muggles magic.

Challenge Level

What does Pythagoras' Theorem tell you about these angles: 90Â°, (45+x)Â° and (45-x)Â° in a triangle?

Challenge Level

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.

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There are many different methods to solve this geometrical problem - how many can you find?

Challenge Level

What is the longest stick that can be carried horizontally along a narrow corridor and around a right-angled bend?

Challenge Level

This problem in geometry has been solved in no less than EIGHT ways by a pair of students. How would you solve it? How many of their solutions can you follow? How are they the same or different?. . . .

Challenge Level

Use simple trigonometry to calculate the distance along the flight path from London to Sydney.

Challenge Level

If for any triangle ABC tan(A - B) + tan(B - C) + tan(C - A) = 0 what can you say about the triangle?

Challenge Level

In this 'mesh' of sine graphs, one of the graphs is the graph of the sine function. Find the equations of the other graphs to reproduce the pattern.

Challenge Level

A moveable screen slides along a mirrored corridor towards a centrally placed light source. A ray of light from that source is directed towards a wall of the corridor, which it strikes at 45 degrees. . . .