Unit 3: Geometry Vocabulary

Transversal

A line that cuts across a set of lines or the sides of a plane figure. Transversals often cut across parallel lines.

Angle Bisector

A line which cuts an angle into two equal halves

Angle Addition Postulate

The angle addition postulate states that if B is in the interior of AOC, then m<AOB + m<BOC= m<AOC.

Corresponding Angles

The angles in matching corners are called Corresponding Angles.

Midpoint

The midpoint is the middle point of a line segment.

Angle

The space within two lines or three or more planes diverging from a common point, or within two planes diverging from a common line.

Transitive Property

If a = b and b = c, then a = c

Straight Angle

An angle whose measure is exactly 180°.

Theorem

An assertion that can be proved true using the rules of logic or postulates.

Postulate

A statement that is assumed to be true.

Perpendicular Lines

Lines that are at right angles (90°) to each other.

Equidistant

Something is the same distance away from two points.

Segment Addition Postulate

The distance from one endpoint to the other is the sum of the distances from the middle point to either endpoint.

Supplementary Angles

Two angles that add up to 180°.

Complementary Angles

Two angles that add up to 90°.

Linear Pairs

Two angles that are adjacent (share a leg) and supplementary (add up to 180°).

Parallel Lines

Two lines on a plane that never meet. They are always the same distance apart.

Vertical Angles

Vertical angles are angles opposite one another at the intersection of two lines. Vertical angles are congruent.

Alternate Interior Angles

When two lines are crossed by another line (which is called the Transversal), the pairs of angles • On opposite sides of the transversal • But inside the two lines are called Alternate Interior Angles

Consecutive (Same-Side) Interior Angles

When two lines are crossed by another line (which is called the Transversal), the pairs of angles: • On one side of the transversal • But inside the two lines are called Consecutive Interior Angles

Alternate Exterior Angeles

When two lines are crossed by another line (which is called the Transversal), the pairs of angles: • On opposite sides of the transversal • But outside the two lines are called Alternate Exterior Angles