FORMULABANK

∆ABC

The points A, B, and C form a triangle.

Line segments with the same number of marks are of equal length. The lines in figure a are of equal length. The lines in figure b are also equal.

However, the lines in figure a and b are NOT of the same length.

Lines with the same number of arrows are parallel. The line segments |AB| and |CD| are parallel, which is written as: AB∥CD

Conversely, the line segments |AB| and |BC| are not parallel, which is written as: AB∦BC
 

  |AB|

A line segment is often written with two vertical bars. For example, |AB| represents the line segment from point A to point B.

Angle
It can be written as ∠ABC, where the angle is at point B.

Angles with the same marking are congruent.
If they have no markings, it is not known whether they are congruent.
 

Symbol for parallel lines
For example, AB || CD
Line segment AB is parallel to CD.

Perpendicular to:
AB ⊥ CD
Line segment AB is perpendicular to CD (or vice versa).