# Mastering the World of Angles

Briefly, a Master Angle is a unique protractor-type device that shows and allows measurement and construction of angles from 0° to 360°. It is a round, transparent circle with clearly marked angle measures and a free-moving "hand" that rotates from the center and is marked with a line to show angle measures relative to a marked diameter line on the circle. A unique and welcome feature of the Master Angle manipulative is the inclusion of open "dots" starting at 0° and at each 5° interval around the circle. This allows the young student to just make a dot (point) at the correct measure to draw the angle. It would be a worthwhile tool to use with any early geometry course material. While the workbook was written specifically for the Master Angle (and some activities give detailed instructions for using it to complete them) exercises can be completed with a regular protractor or the 360° Angle Viewer. After an introduction to the subject and importance of angles, including the definition of a few, basic geometric terms, instruction begins with the various types of angles. The book builds concept on top of concept as it progresses, resulting in a pretty thorough survey of basic geometry. It goes much deeper than similar books targeted to this grade level. Besides very complete coverage of angles, including drawing and measuring them, it covers polygons formed by angles (triangles, quadrilaterals, pentagons, hexagons, and octagons), spends a good amount of time investigating angles within circles (plus radius, diameter, chords, circumference, and sections), then turns to real life applications (looking at a ball diamond, planning pool shots, checking angle measures in home construction and on a neighborhood map). Answers to all exercises and suggestions for some additional learning activities are included in the back of the book.

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