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 TOPICS This page:   conic sections,  circles    Search   Dr. Math Shortcuts:   why 360 degrees? See also the Dr. Math FAQ:   circle formulas Internet Library:   conic sections,   circles MIDDLE SCHOOL About Math Algebra    equations    factoring expressions    graphing equations Arithmetic    division    exponents    factorials    factoring numbers    fractions/percents    logarithms Definitions Geometry    2-dimensional      conic sections/        circles      triangles/polygons    3D and higher      polyhedra History/Biography Logic Measurement    calendars/      dates/time    temperature    terms/units Number Sense    factoring numbers    negative numbers    pi    prime numbers    square roots Probability Puzzles Ratio/Proportion Statistics Word Problems Browse Middle School Conic Sections/Circles Stars indicate particularly interesting answers or good places to begin browsing. Selected answers to common questions:     Circle formulas - area, circumference.     Is a circle a polygon?     Why is a circle 360 degrees? Explorations of the Circle [02/09/1999] What is the definition of a circle? How does it relate to pi? What are the important parts of a circle? Finding a Circle's Area Without Pi [02/24/2001] How can I find the area of a circle without using pi? Finding Miles Per Hour [03/06/2002] If a wheel is making 64.2 revolutions per minute, how many miles per hour is it going? Finding the Area of a Circle [3/25/1996] Is there an easy way to do find the area of a circle? Finding the Circumference [11/27/1997] Would you be able to tell me how to work out the circumference of a circle? Finding the Table's Diameter [05/05/2001] A circular table is pushed into the corner of a room so that it touches both walls. On the edge of the table is a scratch 8" from one wall and 9" from the other wall. What is the diameter of the table? Folding a Circle to Get an Ellipse [01/08/2001] How can I prove that taking a point on a circle, folding it to an interior point, and repeating this process creates an envelope of folds that forms an ellipse? Formula for the Area of a Circle [12/17/1998] The formula, and how it works. From Degrees to Radians [09/22/1998] What are radians? How do you convert degrees to radians? History of Circle Area Formula [03/19/2007] Do we know who figured out that pi*r^2 gives the area of a circle? How Did Eratosthenes Measure the Circumference of the Earth? [6/26/1996] Didn't Eratosthenes measure the lengths of shadows of sticks at different locations on the same day and time of the year, so he had two right triangles...? Inscribing a Regular Pentagon within a Circle [04/15/1999] What are the reasons for the steps in inscribing a regular pentagon within a circle with only the help of a compass and a straightedge? Intersection of Circles [10/08/1998] I do not understand the term intersection in geometry. An Introduction to Pi and Its Use in Circle Problems [04/28/2004] The doctor helps a confused student with circle parts, their relation to each other, and pi. Is a Circle a Polygon? [03/07/1999] A circle is not a polygon. Lateral Surface of a Cone [02/10/1999] How do you find the formula for the lateral surface of a right cone? Measuring the Circumference of the Earth [08/16/1999] How did Eratosthenes use a mathematical formula to prove the earth is round? Origin of the 360-Degree Circle [11/10/1999] Did the Babylonians discover the 360-degree circle? Perimeter of an Oval [04/08/1999] What is the perimeter of an oval called? Pi and the Area of Circles [05/11/1997] If pi truly goes on and on forever without repeating, is it impossible to find the exact area of a circle? Placing Coins That Touch [8/7/1996] How many 20-cent coins can you put around a 20-cent coin so that all of them touch? Polygons and Circles [4/3/1996] Is a circle a polygon? Why or why not? Polygons, Infinite Sides, and Circles [04/03/1997] Can a regular polygon with an infinite number of sides be a circle? Radians and Degrees [11/21/1994] Why are radians preferable to degree measures? Radius of a Pizza [8/27/1996] If a pizza has an area of 30 inches, what is its radius? Regions, Chords, and Circles [02/05/1998] A given circle has n chords. Each chord crosses every other chord but no three meet at the same point. How many individual regions are in the circle? The Relation of Perimeter to Area [10/2/1995] I'm puzzled by the ability of two fences with the same perimeter to have very different areas inside them. I realize by LxW an 8' x 10' fence will have more area than a 6' x 12' fence, but WHY? Both fences have 18' surrounding them but different areas. Also does a circle or a square conserve more area with identical perimeters? Rhumb Lines and Great Circle Routes [09/24/1998] Can you explain great circles and rhumb lines and how they relate to shortest distances in geometry? Rounding Pi [06/01/1999] Can you prove that the value of Pi cannot be rounded down to 3.0? Is there an error in the Bible? Simple Closed Curve [05/22/2001] Why is a simple closed curve called just that? Square Inscribed in a Circle [09/28/1997] What percent of the circle is contained within the square? Subtend [07/23/1997] Please give me the definition of the word "Subtends." Symmetry Lines [03/30/2000] How many symmetry lines are in a circle? Three Cuts and Seven Pieces [01/18/1999] Is there any way that you can cut a pie into seven pieces with just three straight cuts? Traceable Mathematical Curves [10/27/1997] Is there any way to tell just by looking if a curve is traceable or not? Is there some property of a curve that will tell you this? Do curves have formulas? Tracing an Ellipse [08/17/1997] How do you form an ellipse using 3 points? Uses of Ellipses [04/02/2003] Where are ellipses found in real life? Walking Around the World [08/18/1999] How much farther does a man's head go than his feet when he walks around the world? Is this a trick question? Ways to Remember the Meaning of Circumference, Radius, Diameter, and Chord [03/18/2004] If the minute hand touched the edge of the clock, would it be most like a diameter, radius, circumference, or chord of a circle? I have a hard time remembering what each of those means. What is Circumference? [06/25/2001] My friend told me it's somewhat like the measurement of the outside of a circle, but I don't understand that. Page: []

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