Geometry Review Flash Cards
A point is like a star in the night sky. However,
unlike stars, geometric points have no size. Think
of them as being so small that they take up zero
amount of space.
• A point may be represented by a dot on a
piece of paper.
• A point is usually named with a capital
letter…A
A
B
C
Line: Through any two points there exists exactly
one LINE. That is … two points define a line.
• A “straight” line extends forever in both
directions.
• The name of a line passing through points A
suur
and B can be written as “line AB” or as AB .
• It may also be referred to as “line BA.”
D
B
A
C
Endpoints: An endpoint is a point used to define
a line segment or ray.
Rays: We may think of a ray as a “straight” line
that begins at a certain point and extends forever
in one direction.
• The point where the ray begins is known
as its endpoint.
• The name of a ray with endpoint A anduuur
passing through point B is “ray AB or AB .
The arrowhead denotes the direction the
ray extends in; there is no arrow head over
the endpoint.
D
B
A
Geometry Review Flash Cards
B
A
Opposite Rays: Two rays with a common
endpoint that form a straight line.
C
uuur
suur
uuur
BA and BC make AC
Collinear Points: Points through which one line
can be drawn. Collinear points lie on the same
line.
B
A
C
D
C
Non-Collinear Points: Three or more points that
do not lie on the same line.
A
Plane: Can be thought of as a flat surface
extending infinitely in all directions.
• Through any 3 non-collinear points there
exists a plane.
• A plane has no thickness.
• Planes are usually represented by a shape
that looks like a tabletop or a parallelogram.
• A plane is named by a single letter (plane m)
or by three non-collinear points (plane ABC).
Intersecting lines: The term intersect is used
when lines, rays, line segments or figures meet,
that is, they share a common point (point of
intersection).
B
m
C
B
A
D
Geometry Review Flash Cards
n
Perpendicular lines: Two lines that intersect to
form right angles (angles that have a measure of
90 degrees). A square at the point of intersection
denotes a right angle. We write it with the ⊥
symbol. We say line n is perpendicular to line m;
we write it as line n ⊥ line m.
m
1
Parallel lines: Two lines in the same plane that
never intersect (have no points in common) are
called parallel lines. We write is with the ⏐⏐
symbol. We say line 1 is parallel to line 2; we
write it as line 1 ⏐⏐ line 2.
An angle is formed by two rays with a common
endpoint called the vertex of the angle. The rays
are called the sides of the angle.
• Three letters can be used to name an angles
such as ∠ ABC. The middle letter will always
denote the vertex of the angle.
• An angle can also be named with a number,
for example ∠ 1 or ∠ 2.
Right angle: An angle whose degree measure is
90.
Acute angle: An angle whose degree measure
is greater than 0 and less than 90.
2
A
B
1
C
Geometry Review Flash Cards
Obtuse angle: An angle whose degree measure
is greater than 90 and less than 180.
Straight angle: An angle whose degree
measure is 180.
Congruent angles: Angles that have the same
measure.
A linear pair of angles is a pair of adjacent
angles who share a common ray and are
supplementary. The opposite rays form a straight
line.
Supplementary angles are two angles whose
measures combined equal 180 degrees.
Complementary angles are two angles whose
measures combined equal 90 degrees.
∠ ABC
≅
∠ PQR.
Geometry Review Flash Cards
Adjacent angles: Two angles are adjacent if and
only if they share a common side.
2
1
m∠ 1 = m∠ 2
Bisector of an angle: A ray that divides an angle
into two congruent angles.
1
2
m∠1 = m∠3
Vertical angles: Whenever two lines intersect to
form four angles, the non-adjacent angles are
called vertical angles. If two lines intersect, then
the vertical angles are congruent.
A transversal line intersects two other coplanar
lines. We say that transversal line t intersects
lines a and b. It forms two types of angles:
• Interior angles
• Exterior angles
m∠2 = m∠ 4
4
1
a
b
3
2
t
Geometry Review Flash Cards
m∠3 = m∠6
If two parallel lines are cut by a transversal,
alternate interior angles are congruent.
Alternate interior angles are interior angles on
the opposite sides of the transversal that do not
have a common vertex.
m∠4 = m∠ 5
1 2
3 4
5 6
7 8
m∠1 = m∠8
m∠2 = m∠ 7
If two parallel lines are cut by a transversal,
alternate exterior angles are congruent.
3
Alternate exterior angles are exterior angles on
the opposite sides of the transversal that do not
have a common vertex.
If two parallel lines are cut by a transversal,
corresponding angles are congruent.
Corresponding angles: one interior angle and
one exterior angle that are on the same side of
the transversal and do not have a common
vertex.
7
1 2
4
5 6
8
m∠1 = m∠5
m∠3 = m∠7
m∠2 = m∠ 6
m∠4 = m∠ 8
1 2
3 4
7
5 6
8