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**BASIC ELEMENTS OF GEOMETRY**

Think of geometry as a skyscraper. At its foundation are three basic terms: point, line and plane. These terms are used to define other geometric terms. All these terms are the steel beams of the skyscraper, built carefully upon one another and upon the foundation of the three basic terms. But no matter how firm the foundation, the skyscraper won’t stand unless its beams are carefully connected. In geometry, we connect geometric terms with relationships. Using your foldable, we will go over review the basic terms along with connecting relationships that will be needed for the material we will cover in Chapter 9: Represent Geometry with Algebra. Teacher note: Encourage students to take notes in their Foldable as you progress through this presentation.

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FOLDABLE This slide is to make sure students have put their foldables together correctly. Please run the pdf file two-sided. (Each student should receive 4 sheets of paper)

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**Basic Elements of Geometry**

Geometric terms

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Point Definition: a location in space. A point is named by a capital letter, and its location may be indicated by a dot. Write: A Say: Point A

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Point A point is named by its coordinates, and its location may be indicated by a dot. Write: P Say: Point P

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Line Definition: a set of points that form a straight path extending infinitely in two directions. The directions are opposite of each other. Write: Say: Line AB

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Line Segment Definition: a part of a line that has two endpoints and a definite length A B Write: Say: Line segment AB

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Ray Definition: a set of points that has one endpoint and extends infinitely in one direction A B C Write: Say: Ray AB or Ray AC

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Angle Definition: a geometric figure made up of two rays of two line segments that have the same endpoint. The common endpoint is the vertex. Write: Say: Angle ABC or Angle B

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Plane Definition: a flat surface that extends without end (infinitely) in all directions. Write: Plane A Say: Plane A A

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**Basic Elements of Geometry**

ANGLES

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Angle Definition: a geometric figure made up of two rays of two line segments that have the same endpoint. The common endpoint is the vertex.

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ACUTE ANGLE Angles that have a measure that is less than 90 degrees.

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RIGHT ANGLE Angles that have a measure that is exactly 90 degrees.

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OBTUSE ANGLE Angles that have a measure that is greater than 90 degrees but less than 180 degrees.

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STRAIGHT ANGLE Angles that have a measure that is exactly 180 degrees.

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**Basic Elements of Geometry**

TRIANGLES

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Triangle Definition: a geometric figure made up of three rays or three line segments. Write: Say: Triangle ABC or Triangle BCA or Triangle CAB

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ACUTE TRIANGLE A triangle composed of three acute angles.

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RIGHT TRIANGLE A triangle composed of one right angle and two acute angles.

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OBTUSE TRIANGLE A triangle composed of one obtuse angle and two acute angles.

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SCALENE TRIANGLE A triangle with no congruent sides and no congruent angles.

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ISOSCELES TRIANGLE A triangle with at least two congruent sides and at least two congruent angles.

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EQUILATERAL TRIANGLE A triangle with three congruent sides and three congruent angles.

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**Basic Elements of Geometry**

QUADRILATERALS

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Quadrilateral Definition: a geometric figure made up of four sides and four angles

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RECTANGLE A quadrilateral with four right angles. Opposite sides are equal in length.

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SQUARE A quadrilateral with four right angles. All sides are equal in length.

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PARALLELOGRAM A quadrilateral with opposite sides that are parallel. Opposite sides are equal and opposite angles are equal.

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RHOMBUS A quadrilateral with opposite sides that are parallel. Opposite sides are equal in length and opposite angles are equal in measure. All sides are equal in length.

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TRAPEZOID A quadrilateral with two sides are parallel and two sides are not parallel.

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KITE A quadrilateral with two pairs of consecutive congruent sides.

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**SYMBOLS and ABBREVIATIONS**

Basic Elements of Geometry SYMBOLS and ABBREVIATIONS

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**Basic Elements of Geometry**

COMMON POLYGONS

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Polygons: Triangle (3 sides) Quadrilateral (4 sides) Pentagon (5 sides) Hexagon (6 sides) Heptagon (7 sides) Octagon (8 sides) Nonagon(9 sides) Decagon (10 sides) Dodecagon (12 sides)

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