September 4

Introduction to Geometry:
Notation, Terms, and Proofs

Notation | Terms | Axioms | Proofs

Notation

1) Points are denoted in the text by a capital letter. However, you may use upper or lower case if you wish

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2) Lines are denoted:

a) If a line contains two distinct points, such as A and B,

then the line will be denoted by:

b) If a line has no designated points on it,

then the line will be denoted by a script letter, such as line

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3) Rays are denoted by their initial point and another point on the ray. For example,

is denoted by:

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4) Line segments are denoted by their end points. For example,

is denoted by

If just AB is written without the bar, then that means the length of the line segment

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5) Angles are denoted in several ways:

a) If there is no problem identifying which angle it is.

For example:

This angle could be read as either <B or <ABC or <CBA.

The vertex of the angle always is placed in between the letters designating points on the two sides of the angle.

b) If more than one angle is at a vertex, then all three letters MUST be used.

In this example, there are three angles, which could be read as:

1) <ABC or <CBA.
2) <ABD or <DBA

3) <DBC or <CBD

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6) Triangles are always denoted by the letters at the three vertices.

For example:

This triangle could be read as:

However, the order of the vertices is often not important.

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7) Congruence is denoted by:

which is very different from the plain "=" sign. The "=" sign means only size, while the congruence symbol means both shape and size.

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