Definitions in Geometry have to be very precise. They have to answer a very particular set of questions: What is it like? and How is it different? Just like in the sciences, where you see a structured categorization system, geometry groups its object into a hierarchy. We start with a basic set of terms and define more complex terms based on the terms directly before.
For example, even though a rectangle "has" points and lines, these components aren't part of the definition of a rectangle. A rectangle is defined as a quadrilateral with 4 right angles. So a rectangle is in the group "quadrilaterals" - it is like all other quadrilateral - but it's different because it has to have 4 right angles - not every quadrilateral has that.
So we need to practice this precision in definitions. Your job is take a definition and determine if it is a good definition (just right), a weak definition (good but not the best), or a bad definition (wrong). Copy the definition into your response and classify it: good, weak, bad, with a sentence or 2 about why. Then reply to at least one other student's comment. Your reply should be a sentence or two about why you agree or disagree.
1. The radius of a circle is the distance from the circle's center to a point on the circle, and is constant for a given circle.
2. A polyhedron is a closed two-dimensional figure. All of the faces are made up of polygons.
3. An isosceles triangle is a triangle with two equal sides.
4. A circle is the set of all points in a plane that are equidistant from a given point in the plane, which is the center of the circle.
5. A central angle is an angle with its vertex is in the circle.
6. The hypotenuse is the longest side of a triangle.
7. An equilateral triangle is a triangle with three equal sides.
8. A kite is a quadrilateral that has two pairs of sides congruent (the same length).
9. A quadrilateral is a polyhedron with exactly four sides.
10. A scalene triangle is a triangle with all three sides unequal.
11. A square is a quadrilateral with 4 congruent sides.
12. A trapezoid is a quadrilateral that has one pair of opposite sides that are parallel.
13. A watch is a portable timepiece.
14. A platypus is in the Order Monotremata.
15. An ear is the vertebrate organ of smell.
16. A vertex of a polygon is the point where two sides meet.
17. A transversal is a line that passes through (transverses) two parallel lines.
18. A theorem in mathematics is a proven fact.
19. An anaerobe is an organism that grows in the presence of oxygen.
20. An antibody is an immunoglobulin protein produced by B-lymphocytes of the immune system that binds to a specific antigen molecule.
21. A bacteriocide is a class of antibiotics that kills bacterial cells.
22. A cation is a charged ion.
23. A coenzyme (cofactor) is an organic molecule, such as a vitamin, that binds to an enzyme and is required for its catalytic activity.
24. A fungicide is an agent, such as a chemical, that kills fungi.
25. A habitat is a location where a plant or animal lives.
26. A haploid is a cell that contains two sets of chromosomes.
27. A hamada is a very flat desert area of exposed bedrock.
28. A heterotroph is a carnivore.
29. A hurricane is an intense cyclonic storm.
30. A base is any substance with a pH above 7.
31. A neutron is an atomic sub-particle found in the nucleus of an atom
32. A normal fault is a vertical fault where one slab of the rock is displaced up and the other slab down.
33. A Watt is a metric unit of measurement of the intensity of radiation in Watts over a square meter surface (W/m2 or W m-2).
34. An analogy is the comparison of two pairs which have the same relationship.
35. An aphorism is a brief saying embodying a moral, a concise statement of a principle or precept given in pointed words.
36. An onomatopoeia is a word that imitates the sound it represents.
37. A metaphor is the comparison of two UNLIKE things, using like or as.
38. Metonymy is substituting a word for another word closely associated with it.
39. An allusion is a brief reference to a person, event, or place, real or fictitious, or to a work of art.
40. A malapropism is an act or habit of misusing words ridiculously, esp. by the confusion of words that are similar in sound.
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