Geometry Midterm Vocabulary

Area

of a geometric figure is the number of square units it encloses.

Collinear

on the same line

incenter

intersection of the angle bisectors of the triangle, always inside the triangle

Parallel

do not intersect

Right

angle that equals 90 degrees, or triangle with angle that equals 90 degrees

Acute

angle less than 90 degrees, or triangle with angle less than 90 degrees

Complements

two angles that add up to equal 90 degrees

Intercept

point where a line crosses an axis

Perimeter

of a geometric figure is the distance around the figure.

Scalene

triangle with no equal sides

Altitude (of a triangle)

the perpendicular segment from the vertex of a triangle to the line containing the opposite side, an altitude of a triangle can be inside, outside, or on the side of the triangle.

Concurrent

when three or more lines intersect at one point

Isosceles

a triangle with at least two equal sides

Perpendicular (lines)

lines that intersect to form a right angle

Segment

part of a line, consists of two endpoints and all the points between them

Angle

consists of two rays with a common endpoint.

Congruent

(figures)have the exact same shape and size, a flip, rotate (turn), or slide does not affect whether figures are congruent because they still have the same shape and size.

Line

extends in opposite directions without end and has one dimension—length.

Plane

extends in two dimensions without end. The two dimensions are length and width, but no thickness. We represent a plane by a flat surface.

Skew lines

are noncoplanar; they are not parallel and do not intersect.

Biconditional

if and only if statement used when a conditional and its converse are both true

Coplanar

in the same plane

Median (of a triangle)

segment whose endpoints are a vertex and the midpoint on the opposite side (a triangle's three medians are always congruent)

Point

has no dimension (no length, width, or height). It does have a location, or position.

Slope

of a line is the ratio of the vertical change (rise) to the horizontal change (run) between any two points.

Segment Bisector

A line, ray, segment, or plane that intersects a segment at its midpoint

Distance

between points A and B is the absolute value of the difference of their coordinates.

Midpoint

a point that divides, or bisects, a segment into two congruent segments.

Postulate

are statements that we accept as true and do not try to prove.

Supplements

two angles that add up to equal 180 degrees

Circumcenter

The lines that contain the altitudes of a triangle are concurrent at, center of the circle circumscribed about the triangle whose radius is the distance from circumcenter to vertex

Equiangular

all angles are equal

Obtuse

angle larger than 90 degrees, or triangle with angle larger than 90 degrees

Proof

is a logical argument in which each statement is supported by fact, definition, postulate, theorem, etc.

Theorem

are statements that we prove using logic, the foundation above, and other previously proved theorems.

Circumference

The distance around a circle

Equilateral

a triangle with three equal sides

Orthocenter

where The lines that contain the altitudes of a triangle are concurrent at (inside, outside, or on triangle)

Ray

part of a line. It consists of an endpoint and all points of a line on one side of the endpoint.

Transversal

a line that intersects two or more coplanar lines at different points.