Quadrilaterals - Definitions and constructions
Personal definitions of a square
In our class, we discussed your "personal" definitions of a square. Two important take-away messages from this discussion are:
- There are many ways of defining the same object. We need to consider our starting point - Do we already know what a rectangle is? Do we know what a regular polygons is? Or perhaps we only know that square is a quadrilateral?
- Correct definitions may still contain redundant references. For example, defining square as a "regular polygon with four congruent sides and four congruent angles" is correct, although we don't have to list all of these conditions. (Which ones can be dropped?)
Minimal definitions of quadrilaterals
In order to agree on what different quadrilaterals are, we need to agree on their definitions. The following is the list of minimal definitions of quadrilaterals as we are going to use them. Please note the definition of a kite, trapezoid and square - is there something unexpected there?
Quadrilateral - a four-sided polygon
Kite – quadrilateral with two distinct pairs of adjacent congruent sides
Trapezoid - a quadrilateral with at least one pair of parallel sides
Isosceles trapezoid - a trapezoid with congruent base angles
Parallelogram – a quadrilateral with two pairs of parallel sides
Rhombus – a quadrilateral with four congruent sides
Rectangle – a quadrilateral with three right angles
Square – a quadrilateral with four congruent sides and one right angle
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Constructing quadrilaterals
Knowing the defitions of quadrilaterals, we can now try to construct them. As you will see, construction of quadrilaterals can be quite a challenging task as we are trying to come up with the most general construction for each quadrilateral.
For example, if you are constructing a rhombus, you should be able to manipulate your construction (drag vertices) to create any rhombus you want but no quadrilateral that is not a rhombus.
Sometimes you'll see that your construction "breaks down" and you end up with a line or no shape at all. This should be fine as long as you are able to manipulate your quadrilateral and:
- Create any quadrilateral of the chosen category (kite, rhombus, parallelogram,...).
- Whenever your shape is a quadrilateral, it is a quadrilateral of that category.