Geometry Basic Terms Unit 1 Vocabulary

Angle Two rays with the same vertex that are not opposite.

Adjacent Angles Two coplanar (same plane) angles that have a common side and a common vertex (point) but no common interior (inside) points Next to each other

Complementary Angles Sum of their angles = 90 degrees

Supplementary Angles Two angles that add up to 180 degrees

Vertical Angles Two angles whose sides form pairs of opposite rays Non-adjacent angles formed by intersecting lines.

Parallel Lines Lines on the same plane (coplanar) and do not intersect (cross, touch, meet) Distance between the two lines are the same. II

Vertex The point where two lines intersect.

Perimeter Units around a plane Sum of the length of sides Distance around an object Units

Acute Angle Angle whose measure is less than 90 degrees but greater than 0 degrees

Obtuse Angle Angle whose measure is more than 90 degrees and less than 180 degrees.

Right Angle Angle whose measure is 90 degrees

Bisect Divide into two congruent halves Cut in half

Straight Angle Angle whose measure is 180 degrees Think a straight line

Point A location No size Undefined Point A

Line Undefined Series of points that extends in two opposite directions Never ends

Collinear Points Points that lie on the same line

Ray Part of a line with one endpoint One end goes on forever, without end

Opposite Rays Two collinear rays with the same endpoint Form a line

Segment Part of a line consisting of 2 points

Endpoint Beginning or end of a line segment or ray.

Plane Flat surface that has no thickness Has no end Not collinear points Plane ABC, Plane ABCD

Coplanar Points and lines on the same plane

Midpoint Point that bisects (divide) the segment into 2 congruent segments Point in the middle

Angle Bisector Ray that divides an angle into 2 congruent angles

Perpendicular Lines Two lines that intersect (cross) to form right angles (90 degrees)

Perpendicular Bisector Line, segment or ray that is perpendicular to the segment at its midpoint

Congruent Angles Angles that have the same measure < AMG ≅ < GMB

Congruent Segments Segments that have the same length ≅

Skew Lines Lines that are NOT parallel, DO NOT intersect, or DO NOT lie on the same plane (noncoplanar) Line AG is skew to line EB