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## For purposes down the road,

## here’s a brief review of

## 2-dimensional geometric shapes

## that are polygons.

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*For more go through the DOOR.*

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For most of you (as well as me) this is an–abbreviated–review of some basic geometric concepts. (We’ve adapted definitions provided from the Oxford Internet Dictionary.) We will refer to such shapes later on.

*[Pardon the sloppy presentation. With our new server we can’t untangle it.]*

**polygon** | ˈpälēˌɡän | noun *Geometry *a plane [2- dimensional] figure with at least 3 straight sides and angles, and typically 5 or more.

**rhombus** | ˈrämbəs | noun (plural or rhombuses or **rhombi **| -ˌbī, -ˌbē | ) *Geometry *a [2-d] parallelogram with opposite equal acute angles, and opposite

equal obtuse angles, and 4 equal sides. [The exception is if all angles are 90 degrees as in a square.

**square **| skwer | noun ** **a plane figure with 4 equal straight sides and 4 right angles.

** parallelogram** | ˌperəˈleləˌɡram | noun a 4-sided plane rectilinear figure with opposite sides parallel.

** rectangle **| ˈrekˌtaNGɡəl | noun a plane figure with 4 straight sides and 4 right angles, especially 1 with unequal adjacent sides, in contrast to a square.

** triangle** | ˈtrīˌaNGɡəl | noun a plane figure with 3 straight sides and 3 angles.

** pentagon** | ˈpen(t)əˌɡän | noun a plane figure with 5 straight sides and five angles.

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** CONCLUSIONS:**

(1) Rh, S, Pa, Re, T, and Pe (above) are all polygons. There are other polygons such as “hexagon” and “decagon.” We’ll just consider the 6 polygons above, however.

(2) All these, as stated, involve only straight lines and no curves, arcs, or circles.

(3) A square is a special kind of rhombus.

(4) A rectangle is a special kind of parallelogram.

(5) Note: “Equal” or “equilateral” is a common adjective used with polygons. In an *equilateral triangle* or *equilateral pentagon*, the polygon has 3 and 5 equal sides and angles, respectively. The sides of all polygons join in a “connecting fence,” though sides and angles may vary.

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