Triangles and Transversals Triangles
A three-sided polygon.
Symbol → ▵
You name it ▵ ABC. Total Angle Sum of a Triangle
The interior angles of a triangle add up to 180 degrees.
Symbol = Acute Triangle
A triangle that contains only angles that are less than 90 degrees. Obtuse Triangle
A triangle with one angle greater than 90 degrees (an obtuse angle). Right Triangle
A triangle with one right angle (90 degrees). Vertex
The common endpoint of two or more rays or line segments. Complementary Angles
Two angles whose measures have a sum of 90 degrees. Supplementary Angles
Two angles whose measures have a sum of 180 degrees. Perpendicular Lines Lines that intersect to form a right angle (90 degrees).
Symbol = Parallel Lines
Lines that never intersect.
Arrows are used to indicate lines are parallel.
Symbol = || Transversal Lines
A line that cuts across two or more (usually parallel) lines. Intersect
The point where two lines meet or cross. Vertical Angles
Angles opposite one another at the intersection of two lines. Vertical angles have the same angle measurements. Interior Angles
An angle inside a shape. Exterior Angles
Angles outside of a shape. Alternate Interior Angles
The pairs of angles on opposite sides of the transversal but inside the two lines. Alternate Exterior Angles
Each pair of these angles are outside the lines, and on opposite sides of the transversal. Corresponding Angles
The angles in matching corners. Reflexive Angles
An angle whose measure is greater than 180 degrees and less that 360 degrees. Straight Angles
An angle that measures exactly 180 degrees. Adjacent Angles
Angles with common side and common vertex without overlapping. Angles that are next to one another.