ahh
Te Arapiki Ako
"Towards better teaching & learning"
 You must sign up before you can log in to this revamped site for the first time. Your log in details from our older site will no longer work. User Name / Email Address: Password: Remember me until I logout

# Areas of circles

 Add to your favourites Remove from your favourites Add a note on this item Recommend to a friend Comment on this item Send to printer Request a reminder of this item Cancel a reminder of this item
Last updated 26 October 2012 15:30 by NZTecAdmin
Areas of circles (PDF, 36 KB)

Measurement progression, 5th step

## The purpose of the activity

In this activity, the learners develop an understanding of how to calculate the area of a circle. This activity should follow the Circumferences activity above.

## The teaching points

• The learners understand that the area of a circle can be calculated by multiplying the radius squared by pi (π).
• The learners are able to estimate the area of a circle.
• The learners can identify the diameter, radius and circumference of a circle.
• The learners know that the radius is half the diameter.
• The learners know that the circumference of a circle is approximately three times, and exactly pi (π) times, the diameter.
• The learners understand that r squared (r2) means r x r.

## Resource

• A variety of sizes of paper circles – a pair of each size.
• Scissors.

## The guided teaching and learning sequence

1. Ask the learners to discuss what they already know about the area of the circle. Record their responses on the board, including the formula A = πr2 if it is given.

2. Give each pair of learners two paper circles of the same size and ask them to draw a diameter and a radius on one circle.

3. Discuss what they have done:

“Does a diameter always pass through the centre point?” (yes)
“Does the radius always end at the centre point?” (yes)
“What is the relationship between the radius and the diameter?” (The diameter is twice the radius.)
“Identify the circumference of the circle.”
“Is there a relationship between the diameter and the circumference?” (yes)
“What is the relationship approximately and what symbol is used to describe it?” (The circumference is approximately three times the diameter and the symbol used to describe it is π.)

4. Ask the learners to discuss how they could estimate the area of their circle.

You may need to remind them that the area is the number of square units needed to completely cover the circle.

Methods of estimation could include:

• estimating the number of square centimetres that would fit on the circle
• estimating what fraction of a square metre the circle is
• calculating the area of the square that the circle fits within, the side being the diameter of the circle, as an estimation of the area of the circle.

5. Ask the learners to estimate the area of their circle and record their estimation.

6. Explain to the learners that there is a formula for calculating the area of a circle and refer to it if it was given at the beginning of the session. Say that the learners are going to undertake an activity to justify the use of that formula to calculate the area of a circle. Ask them to fold the circle in half, in half again, and then in half again. When opened there will be 8 ‘sectors’. Ask the learners to cut out the sectors and reassemble them to form an approximate parallelogram. Draw the required shape on the board. Alternatively you may demonstrate the process.

7. Ask the learners to compare their first circle with the parallelogram and ask:

“Is the area of the (approximate) parallelogram the same as the area of the circle?” (yes)
“How would you find the area of the parallelogram?” (Multiply the base by the height at right angles between them.)
“What part of the circle is the height of your parallelogram?” (radius)
“What part of the circle are the two long sides of your parallelogram?” (circumference)
“What part of the circle is one of the long sides of the parallelogram?” (half the circumference)
“If the full circumference is 2πr, what is half the circumference?” (πr)
“If the area of the parallelogram is found by multiplying the base by height, write this using π and r.” (π x r x r)
“In what other ways can you write r x r?” (r2)
“Do you accept that you can use A= π x r2 to find the area of a circle?”

8. Write the formula for the area of a circle A = πr2 and ask the learners to use this formula to calculate the area of their circle.

## Follow-up activity

Pose problems that require the learners to use the formula discussed above.

29 December 2016 04:30
thank you for sharing quite important points regarding to teaching of mathmatics and, http://www.besstessays.net/ recommends that that post will solve the problem which was done by many persons commonly.
18 January 2017 22:58
good download and install numerous apps from the Play Store, https://iplaystoreapp.com been discussing different facets of the Google Play Store nice.
27 January 2017 00:10
good is firmly authorized out of the Google Play Shop every single https://iplaystoreapp.com/google-play-store-for-pc-download-windows-8-10-7-free as Android market. It is generally an internet electronic shop nice.
27 January 2017 20:42
good Incapable to Install Tutu App or won&#39;t download TuTu https://tutuappguide.com/tutuapp-pokemon-go-installation-not-working-solved need to be able to appreciate Pokemon Go from Tutuapp nice.
25 February 2017 20:16
Play styles and preferences across xbox one and microsoft Pcgames xbox live gold free at the heart of direct x12 is than ever before, maximizing use of exisiting graphics hardware.
25 February 2017 20:17
Thanks for the xbox http://xblivecodes.net for xbox free lives codes
10 March 2017 18:45
Play store update: Allowing its users to download apps is just one of the tasks of play store but not the only task. Updating is one of the main functions of play store
https://playstore-app.org/play-store-update/
28 March 2017 18:15
Retrouvez les chaussures homme Nike en promo en ligne sur ▻Zalando ... Nike Performance - AIR MAX 2017 - Chaussures de running neutres - blue/white/. air max pas cher http://www.musclegaintruths.com/
28 March 2017 18:16
Retrouvez les chaussures homme Nike en promo en ligne sur ▻Zalando ... Nike Performance - AIR MAX 2017 - Chaussures de running neutres - blue/white/. air max pas cher http://www.musclegaintruths.com/
31 March 2017 19:31
Articles of interest can certainly make his readers was, his example as I see in this yard, I was quite helpful at all, thank you sir.

http://www.europahaus-ev.de/
12 April 2017 05:56
Blog is very good, I like it! Thank you for you sharing!Your blog is really helps for my search and i really like it.

http://www.magnaflowexhaustshop.com/

Thank you!!
12 April 2017 06:02
good
13 April 2017 23:30
locate in Mobdro apk 2017 to your good friend and https://mobdroappz.com/ the subscription from the freemium application.
21 April 2017 19:10
Math games are really fun to play as this games are based on maths and you can play this cool mathematics games for many hours and also your kids will also love to play this cool math games.
09 June 2017 22:50
Home display go into your Apps, Es File Explorer, click http://livenettvapk.org/ Sports, Entertainment, News, Cooking, Music, Kids.
26 June 2017 16:11
that&#39;s interesting . I like them very much. Thank you for sharing
I hope you will share more interesting things like this .
-------------------------------------------------
==> http://pdgreenpark.vn
==> https://goo.gl/qy48zz
==> https://github.com/Huystevent
==> https://pdgreenpark.tumblr.com
28 June 2017 18:50
Time to praise the http://www.web-farm.co.uk rolex replica father of love IWC Father&#39;s Day masterpiece watch selection http://www.acornpc.co.uk replica watches uk Portugal series manual on the eight-day power reserve http://www.mmwatches.co.uk swiss replica watches "75 anniversary" Special Edition: for the father to provide long power reserve
28 June 2017 18:52
http://watches.rolexreplicauk.co.uk rolex replica Portugal series manual eight-day power reserve http://www.replicaonlines.me.uk replica watches uk
"75th anniversary" special edition of the classical atmosphere, with http://www.perfectreplicawatch.me.uk swiss replica watches up to eight days of reliable power, for the father to provide long power reserve.