Finding the area of circles

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Presentation transcript:

Finding the area of circles

Radius vs. Diameter A RADIUS is the distance from the center of a circle to any point on the outside! A DIAMETER is the distance across the center of a circle, from one side to the other! REMEMBER: If a circle is cut in HALF, it will DIE…this means a line cutting a circle in HALF is the DIAMETER!!!

Is the FRACTION form of PI….just in case you need it!!! : D Whats that sign??? A =  r2 To find the AREA of a circle we have to square the radius and then times it by PI. A = 3.14 ● r ● r 22 This is a GREAT way to write the formula so that you can remember it easily.ut But you need to know what r2 means when you see the formula normally! 7 Is the FRACTION form of PI….just in case you need it!!! : D

Lets try one!!! Plug the numbers in 1st ! A =  r2 A = 3.14 x 2 x 2 2 ft. Do the square numbers A = 3.14 x 4 3.14 x 4 12.56 A = 12.56 ft2

What’s different here??? A =  r2 Change the Diameter to a Radius 1st !!! A = 3.14 x 8 x 8 16 in Do the square numbers A = 3.14 x 64 3.14 x 64 1256 +1884x 200.96 A = 200.96 in2

What if you have a semi-circle??? A = ½  r2 Since only half the circle is used, use HALF of PI - 1.57 A = 1.57 x 4 x 4 4 m A = 1.57x 16 1.57 x 16 942 +157x 25.12 A = 25.12 in2