If area is how many unit squares fit within a shape, how do we fit squares in a circle? Because squares don’t fit evenly into circles, we don’t usually get an even answer when we’re looking for the area of a circle. We also need to use \( \pi \) (pi). The following video explains how to find the area of a circle from the radius.
Video Source (06:44 mins) | Transcript
Let \( r = radius \)
\( Area = \pi r^2 \)
Standard Mathematical Formats with Pi
When pi is part of a solution there are two ways you can display the solution. The first way is to write the number part of the solution multiplied to pi such as \( 13\pi ft \) or \( 5.3\pi cm\). We generally write the number then pi and then the units.
The second way to show your solution is to multiply the number portion of the solution to pi and then round to an appropriate place value. (Example: \( 13\pi ft = 40.84 ft \) rounded to the nearest hundredth)
In this course, we will always multiply pi into our solution and round to an appropriate place value. Just know that the other way is commonly used, and you may see it in textbooks or other classes as a standard way to write solutions when pi is involved.
- Khan Academy: Area of a Circle (4:01 mins; Transcript)
- Khan Academy: Area of a Circle Intuition (9:25 mins; Transcript)
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