The formula for the area of a circle is A = πr2, or pi times r squared (radius squared). I show how to use the formula in several example situations. We then solve a few word problems. Lastly, I show a simple proof for the formula, based on dividing the circle into many sectors, which are close to triangles. Rearranging those sectors, we get a shape that is close to a parallelogram. Starting from the area of the parallelogram, we get the familiar formula for the area of a circle.
Pi and the circumference of a circle — video lesson
Math Mammoth Geometry 2 — a self-teaching worktext with explanations & exercises (grades 4-5)
Back to the geometry videos index
Math Mammoth TourConfused about the different options? Take a virtual email tour around Math Mammoth! You'll receive: An initial email to download your GIFT of over 400 free worksheets and sample pages from my books. Six other "TOURSTOP" emails that explain the important things and commonly asked questions concerning Math Mammoth curriculum. (Find out the differences between all these different-colored series!)This way, you'll have time to digest the information over one or two weeks, plus an opportunity to ask me personally about the curriculum. A monthly collection of math teaching tips & Math Mammoth updates (unsubscribe any time) We respect your email privacy.
Note: You will FIRST get an email that asks you to confirm your email address. If you cannot find this confirmation email, please check your SPAM/JUNK folder. |
"Mini" Math Teaching CourseThis is a little "virtual" 2-week course, where you will receive emails on important topics on teaching math, including:
- How to help a student who is behind You will also receive: A GIFT of over 400 free worksheets and sample pages from my books right in the very beginning.![]() We respect your email privacy.
Note: You will FIRST get an email that asks you to confirm your email address. If you cannot find this confirmation email, please check your SPAM/JUNK folder. |
Maria's Math TipsEnter your email to receive math teaching tips, resources, Math Mammoth news & sales, humor, and more! I tend to send out these tips about once monthly, near the beginning of the month, but occasionally you may hear from me twice per month (and sometimes less often). Peek at the previous tips here. You will also receive:
We respect your email privacy.
|