2D shapes and their properties

There are 151 NRICH Mathematical resources connected to 2D shapes and their properties
Pent
problem

Pent

Age
14 to 18
Challenge level
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The diagram shows a regular pentagon with sides of unit length. Find all the angles in the diagram. Prove that the quadrilateral shown in red is a rhombus.
Hex
problem

Hex

Age
11 to 14
Challenge level
filled star empty star empty star
Explain how the thirteen pieces making up the regular hexagon shown in the diagram can be re-assembled to form three smaller regular hexagons congruent to each other.
Tricircle
problem

Tricircle

Age
14 to 16
Challenge level
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The centre of the larger circle is at the midpoint of one side of an equilateral triangle and the circle touches the other two sides of the triangle. A smaller circle touches the larger circle and two sides of the triangle. If the small circle has radius 1 unit find the radius of the larger circle.
Rhombus in Rectangle
problem

Rhombus in Rectangle

Age
14 to 16
Challenge level
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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.
2001 Spatial Oddity
problem

2001 Spatial Oddity

Age
11 to 14
Challenge level
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With one cut a piece of card 16 cm by 9 cm can be made into two pieces which can be rearranged to form a square 12 cm by 12 cm. Explain how this can be done.
The medieval octagon
problem

The medieval octagon

Age
14 to 16
Challenge level
filled star filled star empty star
Medieval stonemasons used a method to construct octagons using ruler and compasses... Is the octagon regular? Proof please.
Holly
problem

Holly

Age
14 to 16
Challenge level
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The ten arcs forming the edges of the "holly leaf" are all arcs of circles of radius 1 cm. Find the length of the perimeter of the holly leaf and the area of its surface.
Lying and Cheating
problem

Lying and Cheating

Age
11 to 14
Challenge level
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Follow the instructions and you can take a rectangle, cut it into 4 pieces, discard two small triangles, put together the remaining two pieces and end up with a rectangle the same size. Try it!
Three four five
problem

Three four five

Age
14 to 16
Challenge level
filled star filled star empty star
Two semi-circles (each of radius 1/2) touch each other, and a semi-circle of radius 1 touches both of them. Find the radius of the circle which touches all three semi-circles.
Floored
problem

Floored

Age
14 to 16
Challenge level
filled star filled star empty star
A floor is covered by a tessellation of equilateral triangles, each having three equal arcs inside it. What proportion of the area of the tessellation is shaded?