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 TOPICS This page:   two-dimensional  geometry    Search   Dr. Math See also the Dr. Math FAQ:   geometric formulas and   naming polygons   and polyhedra Internet Library:   Euclidean/plane   geometry 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 Two-Dimensional Geometry Stars indicate particularly interesting answers or good places to begin browsing. Selected answers to common questions:     Classifying quadrilaterals.     Pythagorean theorem proofs. Circumference vs. Perimeter [05/09/2003] Technically speaking, can the term 'perimeter' apply to a circle in a mathematical context? Classification of Angles by Size [09/30/2008] What do you call an angle that is greater than 180 degrees? Cleaning the Ice [09/09/1997] The hockey rink is a rectangle, 120 ft. by 60 ft. The scraper cleans a 4- ft.-wide strip... on which trip will it have cleaned half the area of the rink? Complementary and Supplementary Angles [09/30/1998] Why are angles called complementary and supplementary? Complementary and Supplementary Angles [10/24/1999] Definitions of complementary and supplementary angles. Complementary or Supplementary? [04/02/2001] I keep getting complementary and supplementary mixed up. How can I remember which is which? Connection Between Circumference and Surface Area [05/08/1998] Can you explain the connection between the circumference of a circle and the surface area of a sphere? Constructing a One-Degree Angle [05/25/2000] Is it possible to contruct a one degree angle using only a straightedge and compass? Converting Areas: Square Feet to Square Inches [03/18/1997] How many square inches are in ten square feet? Converting Square Feet to Square Yards [09/13/1997] I need to know how to change sq. ft. to sq. yds. for carpeting. Converting Square Inches to Square Feet [02/26/1998] How many square inches are in ten square feet? Converting Square Yards to Square Feet [9/12/1996] 57.33 sq. yds. equals ____ sq. ft? Converting to Square Units [01/07/2002] How do I convert 47,224 sq. miles to kilometers? Convex Polygons and Other Questions [1/22/1996] A 7th grade geometry class asks some questions about area and perimeter. Coordinates in the Cartesian Plane [01/21/2005] How do I get the coordinates for a point on a graph? Counting Angles and Rays [8/23/1995] What is the algebraic expression to show the relation of the number of angles created as rays are added from a common point? Counting Rectangles Cut By a Diagonal [06/15/1999] How can we find an equation for the number of unit squares that are cut by a line going from corner to corner on a rectangle? Covering Paper using Index Cards [10/24/2001] What is the maximum area of an 8"x13" sheet of paper that you can cover by using seven 3"x5" standard index cards? Cutting Slits in a Piece of Paper [02/01/2002] How can you cut a hole in a piece of paper so a person can go through it? Defining a Square Centimeter [04/09/2002] Why is the area of a unit square the product of the two sides? Defining Distance Mathematically [10/16/1996] What is wrong with D' = sqrt(X^2 - X'2)? A Definition of Clinometer [12/10/1995] We've been surfing the net to find a definition of 'clinometer' and have been unsuccessful. Definition of Opposite Sides [01/18/2001] What is the formal definition of 'opposite sides' of a polygon? Does a regular pentagon have opposite sides? Does a concave polygon have opposite sides? How can we define it consistent with our intuition? Definition of Oval [06/09/2002] Can you give a precise definition of 'oval'? Degrees and Radians, Explained [03/19/2002] How do you find the degree measure for an angle from pi/60 rad? Degrees in Complementary and Supplementary Angles [10/28/2002] What are complements and supplements? Deriving Pi [05/10/2001] I know that Pi is equivalent to 3.14, but what formulas are used to come up with 3.14? Deriving the Area Formula for a Circle [03/08/2000] Why is the area of a circle the square of the radius times pi? Diagonals and Tiles [11/17/2001] Jay tiled a 15x21' rectangular ballroom with 1 ft. sq. tiles. Then he drew diagonals connecting opposite corners of the room. How many tiles did the diagonals pass through? Diameter Endpoint [01/26/2003] The center of a circle is (-4,7) and one endpoint of a diameter is (2,-1). What is the other endpoint of the diameter? Dimensions [08/30/2001] What are 1-dimensional, 2-dimensional, and 3-dimensional? What's the difference? Distance between Two Points [08/03/1999] I'm trying to find an equation to measure the distance between 2 points on a 3D plane. Dividing Land by Area vs. Perimeter [11/05/1999] What are the advantages of dividing land by area vs. perimeter? Do Parallel Lines Intersect? [3/1/1996] I have heard that parallel lines can in fact intersect. Is this true? Eleven Nets of a Cube [11/15/2001] My teacher says that there are 11 combinations to make a cube without reversing them, but I can only find 6. Eleven Sections of Fence [05/29/2003] I have a grid containing 16 squares. Each square represents 1 acre. I need to draw 11 sections of fence along the dotted lines of the squares so that 4 fields are formed, each containing 4 acres of land. Equable Shapes [04/26/2001] Is there a rule for how to get equable shapes, that is, shapes with the same area and perimeter? Estimating Seating Capacity [05/10/2000] How can I estimate how many chairs can be placed in the seating area of a convention center meeting room that is 80 feet across at the front, 120 feet across at the rear, and 150 feet from front to back? Etymologies of Algebra, Geometry, Trigonometry [10/22/2001] What are the origins and roots of the words geometry, algebra, and trigonometry? Euclid's Parallel Postulate [2/14/1995] We are studying Euclid's Parallel Postulate. Why did mathematicians disagree with him? What other geometries resulted from this disagreement? What postulate replaced the Parallel Postulate? Page: []

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