Geometry for the Classroom

Intended for use in college courses for prospective or in-service secondary school teachers of geometry. Designed to give teachers broad preparation in the content of elementary geometry as well as closely related topics of a slightly more advanced nature. The presentation and the modular format are designed to incorporate a flexible methodology for the teaching of geometry, one that can be adapted to different classroom settings. The basic strategy is to develop the few fundamental concepts of elementary geometry, first in intuitive form, and then more rigorously. The rest of the material is then built up out of these concepts through a combination of exposition and "guided discovery" in the problem sections. A separate volume including the solutions to the exercises is also available.

Intuition.- I1: Geometry is about shapes.- I2:… and more shapes.- I3: Polygons in the plane.- I4: Angles in the plane.- I5: Walking north, east, south, and west in the plane.- I6: Areas of rectangles.- I7: What is the area of the shaded triangle?.- I8: Adding the angles of a triangle.- I9: Pythagorean theorem.- I10: Side Side Side (SSS).- I11: Parallel lines.- I12: Rectangles between parallels and the Z-principle.- I13: Areas: The principle of parallel slices.- I14: If two lines in the plane do not intersect, they are parallel.- I15: The first magnification principle: preliminary form.- I16: The first magnification principle: final form.- I17: Area inside a circle of radius one.- I18: When are triangles congruent?.- I19: Magnifications preserve parallelism and angles.- I20: The principle of similarity.- I21: Proportionality of segments cut by parallels.- I22: Finding the center of a triangle.- I23: Concurrence theorem for altitudes of a triangle.- I24: Inscribing angles in circles.- I25: Fun facts about circles, and limiting cases.- I26: Degrees and radians.- I27: Trigonometry.- I28: Tangent a =(rise)/(run).- I29: Everything you always wanted to know about trigonometry but were afraid to ask.- I30: The law of sines and the law of cosines.- I31: Figuring areas.- I32: The second magnification principle.- I33: Volume of a pyramid.- I34: Of cones and collars.- I35: Sphereworld.- I36: Segments and angles in sphereworld.- I37: Of boxes, cylinders, and spheres.- I38: If it takes one can of paint to paint a square one widget on a side, how many cans does it take to paint a sphere with radius r widgets?.- I39: Excess angle formula for spherical triangles.- I40: Hyperbolic-land.- Construction.- C1: Copying triangles.- C2: Copying angles.- C3: Constructing perpendiculars.- C4: Constructing parallels.- C5: Constructing numbers as lengths.- C6 Given a number, construct its square root.- C7: Constructing parallelograms.- C8: Constructing a regular 3-gon and 4-gon.- C9: Constructing a regular 5-gon.- C10: Constructing a regular 6-gon.- C11: Constructing a regular 7-gon (almost).- C12: Constructing a regular tetrahedron.- C13: Constructing a cube and an octohedron.- C14: Constructing a dodecahedron and an icosahedron.- C15: Constructing the baricenter of a triangle.- C16: Constructing the altitudes of a triangle.- C17: Constructing a circle through three points.- C18: Bisecting a given angle.- C19: Putting circles inside angles.- C20: Inscribing circles in polygons.- C21: Circumscribing circles about polygons.- C22: Drawing triangles on the sphere.- C23: Constructing hyperbolic lines.- Proof.- P1: Distance on the line, motions of the line.- P2: Distance in the plane.- P3: Motions of the plane.- P4: A list of motions of the line.- P5: A complete list of motions of the line.- P6: Motions of the plane: Translations.- P7: Motions of the plane: Rotations.- P8: Motions of the plane: Vertical flip.- P9: Motions of the plane fixing (0,0) and (a,0).- P10: A complete list of motions of the plane.- P11: Distance in space.- P12: Motions of space.- P13: The triangle inequality.- P14: Co-ordinate geometry is about shapes and more shapes.- P15: The shortest path between two points….- P16: The unique line through two given points.- P17: Proving SSS.- Computer Programs.- CP1: Information you’ll need about the CP-pages.- CP2: Given two points, construct the segment, ray, and line that pass through them.- CP3: Given a line and a point, construct the perpendicular to the line through the point, or the parallel to the line through the point.- CP4: Given a segment, construct its perpendicular bisector.- CP5: Given an angle, construct the bisector.- CP6: Given three vertices, construct the triangle and its medians.- CP7: Given three vertices, construct the triangle and its angle bisectors.- CP8: Given three vertices, construct the triangle and its altitudes.- CP9: Given a figure in the plane and a positive number R, magnify the figure by a factor of R.- CP10: Given a figure in the plane and two positive numbers R and S, magnify the figure by a factor of R in the horizontal direction and by a factor of S in the vertical direction.- CP11: Given the center and radius of a circle, and two positive numbers R and S, magnify the circle by a factor of R in the horizontal direction and by a factor of S in the vertical direction.- CP12: TRANSLATIONS: Given a figure in the plane and two numbers a and b, show the motion m(x,y) = (x + a, y + b).- CP13: ROTATIONS: Given a figure in the plane and two numbers c and s, so that c2 + s2 = 1, show the motion m(x,y) = (cx - sy, sx + cy).- CP14: FLIPS: Given a figure in the plane, show the motion m(x,y) = (x, -y).- CP15: Composing a set of two motions.- CP16: Composing a series of motions.- CP17: Given a point and a positive number R, construct the circle of radius R about the point.- CP18: Given three points in the plane, construct the unique circle that passes through all three points.- CP19: Given the center of a circle and a point on the circle, construct the tangent to the circle through the point.- CP20: Given a circle and a point outside the circle, construct the two lines tangent to the circle that pass through the point.- CP21: Given a point X inside or outside the circle of radius one and center O, construct the reciprocal point X’.- CP22: Given two points inside the circle of radius one about (0,0), construct the hyperbolic line containing the two points.