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Area of a semicircle. Finding the area of semi circles.

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Area of a semicircle video

To find the area of a semicircle first you need to find the area of the whole circle and divide your answer by 2, as a semicircle takes up half the space of a circle.

To find the area of the circle use A=π×r2.  (A stands for the area of the circle, π is Pi and r is the radius of the circle).

Let’s take a look at an example.

area-of-a-semicircle-finding-the-area-of-semi-circles

Example 1

Find the area of this semicircle.

Answer

First find the area of the whole circle. Make sure that you use the radius of the circle (the distance halfway across the circle), this is 4 cm as the diameter is 8 cm (the distance all the way across the centre of the circle).

A = π×r2

A= π×42

A= 50.3... cm2

Now all you need to do is divide the answer by 2

50.3... ÷ 2 = 25.1 cm2 (1 d.p)

Example 2

A semicircular shaped doormat has a radius of 7cm. Calculate the area of the doormat.

Answer

To begin with first find the area of the circle by using A = π×r2.

A = π×r2

A= π×72

A= 154.1... cm2

Again, all you need to do now is to divide the area of the circle by 2.

Do this by 154.1 ÷ 2 = 77.1 cm2 (1 d.p)

Extra Tips

If you don’t have a scientific calculator then use Pi as 3.14 on your pocket calculator.

As you do more examples you might just want to use the formula A = π×r2/2. This will means less lines of working out.


Comments

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andrea on March 11, 2013:

Thank this really helped me on my math homework

Palm on May 20, 2012:

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Mikah on April 02, 2012:

I still don't understand this I am only 10 but my teacher has said that this is a question that is going to appear in my exam I don't understand what all the tt things mean sorry

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Johnson on February 14, 2011:

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See ya

dd on January 22, 2011:

thanx you really helped me ace my test

shaz on November 02, 2010:

fantastic very useful thanks.

Soph on October 27, 2010:

Thanks, this really helped me answer a question in an exam paper :)

(: on October 19, 2010:

thank you, this really does help :D

Mark (author) from England, UK on August 11, 2010:

Thanks for your nice comments.

maths teacher on June 10, 2010:

this is very useful thants

:) on June 03, 2010:

Thanks, ;) simple and easy to understand as always, just hope it comes up in my exam =(

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niv on January 02, 2010:

this was really simple and easy to understand, thanks