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2 feet

“R”, the radius, is 1 foot. R. 1 foot. so A =  R 2  3.14 * 1 * 1  3.14 square feet. 2 feet.  means “about equal to”. Click your mouse for the next idea !. How would you calculate the area of this circle ?. ...probably using the formula A =  R 2.

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2 feet

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  1. “R”, the radius, is 1 foot. R 1 foot so A =  R2 3.14 * 1 * 1  3.14 square feet 2 feet  means “about equal to” Click your mouse for the next idea ! How would you calculate the area of this circle ? ...probably using the formula A = R2 Since the diameter is 2 feet, ? The constant , called “pi”, is about 3.14

  2. 2 feet Click your mouse for the next idea ! LETS explore how people figured out circle areas before all this  business ? The ancient Egyptians had a fascinating method that produces answers remarkably close to the formula using pi. ?

  3. 2 feet Click your mouse for the next idea ! The Egyptian Octagon Method Draw a square around the circle just touching it at four points. ? 2 feet What is the AREA of this square ? Well.... it measures 2 by 2, so the area = 4 square feet.

  4. 2 feet Click your mouse for the next idea ! The Egyptian Octagon Method Now we divide the square into nine equal smaller squares. Sort of like a tic-tac-toe game ! 2 feet Notice that each small square is 1/9 the area of the large one -- we’ll use that fact later !

  5. 2 feet Click your mouse for the next idea ! The Egyptian Octagon Method Finally... we draw lines to divide the small squares in the corners in half, cutting them on their diagonals. 2 feet Notice the 8-sided shape, an octagon, we have created ! Notice, also, that its area looks pretty close to that of our circle !

  6. 1 9 1. 18 1. 18 After all, THIS little square has an area 1/9th of the big one... 1 9 1 9 1 9 And so do these four others... 1. 18 And each corner piece is 1/2 of 1/9 or 1/18th of the big one 1. 18 1 9 2 feet Click your mouse for the next idea ! The Egyptian Octagon Method The EGYPTIANS were very handy at finding the area of this Octagon 2 feet

  7. 1 9 1. 18 1. 18 4 pieces that are 1/18th or 4/18ths which is 2/9ths 1 9 1 9 1 9 Plus 5 more 1/9ths 1. 18 1. 18 1 9 2 feet Click your mouse for the next idea ! The Egyptian Octagon Method ...and ALTOGETHER we’ve got... 2 feet For a total area that is 7/9ths of our original big square

  8. We have an OCTAGON with an area = 7/9 of the original square. 7 9 2 feet Click your mouse for the next idea ! The Egyptian Octagon Method FINALLY... Yep, we’re almost done ! The original square had an area of 4 square feet. 2 feet So the OCTAGON’s area must be 7/9 x 4 or 28/9 or 3 and 1/9 or about 3.11 square feet

  9. AMAZINGLY CLOSE to the pi-based “modern” calculation for the circle ! 3.11 square feet 3.14 square feet only about 0.03 off... about a 1% error !!

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