The circle

The perimeter of a semicircle

Remember that the perimeter is the distance round the outside.

A semicircle has two edges. One is half of a circumference and the other is a diameter.

Diagram of a semicircle with an 8cm diameter

C = \pi d

= 3.14 \times 8

= 25.12cm

Remember this is the circumference of the whole circle, so now we need to half this answer.

25.12 \div 2 = 12.56cm

Total perimeter = 12.56 + 8 = 20.56cm

Area of a circle

For any circle with radius, r, the area, A, is found using the formula:

A = \pi {r^2}

Diagram of a circle with a radius of 12cm

A = \pi {r^2}

= 3.14 \times 12 \times 12

= 452.16c{m^2}

The area of a semicircle

A semicircle is just half of a circle. To find the area of a semicircle we calculate the area of the whole circle and then half the answer.

Diagram of a semicircle with an 4cm diameter

A = \pi {r^2}

= 3.14 \times 4 \times 4

= 50.24c{m^2}

Area of semicircle = 50.24 \div 2 = 25.12c{m^2}

The area of a combined shape

This shape is made up of a rectangle and a semicircle.

To find the total area we just find the area of each part and add them together.

Combined rectangle and semicircle measuring 20mm x 30mm

Area of the rectangle = length x breadth

= 20 \times 30

= 600m{m^2}

Area\,of\,circle = \pi {r^2}

= 3.14 \times 10 \times 10

= 314m{m^2}

Area\,of\,semicircle = 314 \div 2 = 157m{m^2}

Total\,area = 600 + 157

= 757m{m^2}