Ask Dr. Math High School Archive

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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 and   segments of circles Internet Library:   conic sections,   circles HIGH SCHOOL About Math Analysis Algebra    basic algebra    equations/graphs/      translations    linear algebra    linear equations    polynomials Calculus Complex Numbers Calculators/    Computers Definitions Discrete Math    permutations/    combinations Exponents    Logarithms Fibonacci Sequence/   Golden Ratio Fractals Functions Geometry    Euclidean/plane      conic sections/        circles      constructions      coordinate plane      triangles/polygons    higher-dimensional      polyhedra    non-Euclidean    practical geometry    symmetry/tessellations History/Biography Interest Logic Negative Numbers Number Theory Physics/Chemistry Probability Projects Puzzles Sequences/Series Sets Square/Cube Roots Statistics Transcendental   Numbers Trigonometry Browse High School Conic Sections, Circles Stars indicate particularly interesting answers or good places to begin browsing. Selected answers to common questions:     About ellipses.     Find the center of a circle.     Is a circle a polygon?     Volume of a tank.     Why is a circle 360 degrees? Area under Arc of Circle [02/27/2001] Calculate the area delimited by the arc of a circle and the chord of that arc, given only the length of the chord and the length of a line, perpendicular to the chord, running from the middle of the chord to the edge of the circle. Bounding Rectangle for an Ellipse [6/28/1996] I would like to know if there is a general equation for a bounding rectangle of an ellipse. Building a Circular Horse Pen [06/16/2002] My Dad and I are building a round pen for our horse. We have 16 16ft. panels and a 10 ft. gate and a 4ft. gate. (270 ft. total) We want to use a radius and mark the places to dig holes for each post that will support the panels, but we don't know how long the radius should be. Can you help? Building a Cone [10/28/2001] I am trying to find a formula for building a cone for a chimney flashing. It should be 21" tall with a top opening of 8", a bottom opening of 20", and a vertical seam overlap of 2". Calculating Circle Radius [01/29/2001] I am trying to find a formula that will give me the radius of a circle, given only the length of an arc on that circle and the chord length of that arc. Calculating the Radius from a Chord [08/18/1998] If I know the chord length and chord height, is there a formula for determining the radius of the circle? Can a Circle be a Polygon? [5/22/1996] Could a circle be considered a polygon with an infinite number of sides? Catenary and Parabola Comparison [04/06/2004] What is the difference between a catenary and a parabola? I don't know the difference in shape. Why is the St. Louis arch a catenary and not a parabola? Centering Circles [10/05/2002] Two metal disks need to be centered on each other, but the circle with the larger diameter has the center cut out. How can you center them by knowing the diameters? Center of a Circle from Circumference Points [06/25/1999] How do I figure the center point (Xc,Yc,Zc) of a circle given 2 or more points on its circumference and its radius? Center of Mass of a Semicircle [06/14/1999] Is there a standard formula I can use to know where the center of mass of a semicircle is? Changing Angle of a Tank [06/11/2003] Points A and B represent pressure sensors in fixed positions on the base of a round tank. The chord through CD represents the water level in the tank. Lines a and b are the heights of water registered by each sensor... Chord Proofs [10/07/1997] Prove that in any circle a radius perpendicular to a chord also bisects the chord... a radius that bisects the chord is perpendicular to the chord... chords equidistant from the center of the circle are congruent. Chords From Inscribed Polygons [07/11/2002] An regular polygon is inscribed in a circle of known radius. Each side of the octagon is a chord of the circle. What is the length of each chord? Circle and Polygons: Lines of Symmetry [04/14/1997] How many lines of symmetry are there in a circle? Circle Center's Cartesian Coordinates [03/24/1999] How do you find the Cartesian coordinates of a circle's centers if you know two points on its perimeter? Circle Enclosed by Three Circles [08/18/1999] How can I find the center and radius of a circle that is enclosed by three other circles that all touch each other at one point? Circle Geometry [6/4/1996] Two circles intersect at A and N. One of their common tangents has points of contact P and T. Prove that ]

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