1.5 Writing a Good Definition

1. “When I use a word, “ Humpty replied in a scornful tone, “it means just what I choose it to mean—neither more nor less.” - Alice’s Adventures in Wonderland by Lewis Carroll 1.5 Writing a Good Definition During this lesson, you will: Determine the components of a good definition Define geometric figures Draw and label diagrams to illustrate your definitions Mrs. McConaughy Geometry

2. Before we start writing our own geometric definitions, we need to determine what makes a good definition. EXAMPLE Study the information, and then identify which creatures in the last group are Orks. What makes an Ork an Ork? Explain how you determined this. Mrs. McConaughy Geometry

3. Try defining a few more creatures before you go on to define geometric figures with your team members. Mrs. McConaughy Geometry

4. What makes a good definition? Read the passage about writing a good definition, then…without looking…recall the components of a good definition. The same process which helped you identify Orks from non-Orks can help you write good definitions of geometric figures. • A good definition must be precise. • A good definition classifies an • an object with well-defined similar • things. • A good distinguishes the object • you are defining from other sim- • ilar objects. • A good definition is reversible. • A good definition has no counter- • example. Mrs. McConaughy Geometry

5. EXAMPLE Hexagon Not a Hexagon A hexagon is a polygon with exactly six sides. A polygon with exactly six sides is a hexagon. Mrs. McConaughy Geometry

6. An angle with measure of exactly 90 degrees An angle with measure, m, such that 0<m<90 An angle with measure, m, such that 90<m<180 A point on a segment which divides the segment into 2 congruent segments A ray or segment which divides an angle into two congruent angles Mrs. McConaughy Geometry

7. HOMEWORK Mrs. McConaughy Geometry