GCSE(F),

A **perimeter** is the total lengths of all the lines that form the outside of a shape.

The perimeter of a rectangle consists of adding the four lengths together: 5cm + 3cm + 5cm + 3cm = 16cm

The perimeter of a regular polygon is the number of sides multiplied by the length of one side. A regular hexagon with a side of length 5cm has a perimeter of 6 x 5 = 30cm.

When calculating the perimeter of a compound shape, determine the starting point for the shape and work round the shape in one direction to avoid leaving any sides out of the calculation. Put a mark on corner to show where you have started from to avoid missing or double counting a length.

From the diagram above: 3 + 4 + 5 + 4 + 8 + 8 = 32cm

1. A square is shown below. What is the perimeter of the square?

Answer: 16 cm

Each side is 4cm long. 4 x 4 = 16cm

2. What is the perimeter of this triangle?

Answer: 27.31cm

The sloping side is not indicated: this has to be worked out using Pythagoras` Theorem

*c*^{2} = 8^{2} + 8^{2} = 128

*c* = 11.31

The perimeter = 8 + 8 + 11.31 = 27.31cm

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