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2.1 Properties of Segment
Congruence: Reflexive,
symmetric, and transitive
Reflexive example:
AB = AB
Symmetric example:
AB = BA
Transitive example:
AB = CD; CD= BC therefore
AB = BC
2.2 Properties of Angle
Congruence: Angle congruence is
reflexive, symmetric, and transitive.

Reflexive example:
m<A = m< A

Symmetric example:
m<A = m< B; then m<B = m<A

Transitive example:
m<A = m<B; m<B = m<C; therefore
m<A = m<C


2.3 Right Angle Congruence
Theorem: All right angles are
congruent

Ex:
2.4 Congruent Supplements
Theorem: If 2 angles are
supplementary to the same
angle (or to congruent angles)
then they are congruent.
EX:
m<1 + m<2 = 180
m<2 + m<3 =180
Therefore… m<1= m<3

2.5 Congruent Complements Theorem:
If 2 angles are complementary to the
same angle (or to congruent angles)
then the 2 angles are congruent.
EX:
m<4 + m<5 = 90
M<5 + m<6 = 90
Therefore…
m<4 = m< 6

2.6 Vertical angles theorem:
Vertical angles are
congruent.
EX:
m<1 = m<3
M<2 = m<4

3.1 If 2 lines intersect to form a
linear pair of congruent angles,
then the lines are perpendicular.

EX:
3.2 If 2 sides of 2 adjacent acute
angles are perpendicular, then
they are complementary.

EX:
3.3 If 2 sides of 2 adjacent acute
angles are perpendicular, then
they intersect to form 4 right
angles.

EX:
3.4 Alternate Interior Angles: If 2
parallel lines are cut by a
transversal, then the pairs of
alternate interior angles are
congruent.
EX:
m<3 = m< 5
m<4 = m< 6

3.5 Consecutive Interior Angles: if 2
parallel lines are cut by a
transversal, the n the pairs of
consecutive interior angles are
supplementary.
EX:
m<3 + m<6 =180
m<4 + m<5 =180

3.6 Alternate Exterior Angles: If 2
parallel lines are cut by a
transversal, then the pairs of
alternate exterior angles are
congruent.
EX:
m<1 = m< 7
m<2 = m<8

3.7 Perpendicular Transversal: If a
transversal is perpendicular to 1
of 2 parallel lines, then it is
perpendicular to the others.

EX:
3.8 Alternate Interior Angles
Converse: If 2 lines are cut by a
transversal so that the alternate
interior angles are congruent, then
the lines are parallel
EX:
If m<3 = m<5 or
m<4 = m<6
then r ll s

3.9 Consecutive Interior Angles
Converse: If 2 lines are cut by
a transversal so that the
consecutive interior angles are
supplementary, then the lines
are parallel.
EX:
m<3 + m<6 = 180
m<4 + m<5 = 180
Then r ll s

3.10 Alternate Exterior Angles
Converse: If 2 lines are cut by a
transversal so that the alternate
exterior angles are supplementary,
then the lines are parallel
EX:
m<1 = m<7 or
m<2 = m< 8
then r ll s

3.11 If 2 lines are parallel to the
same line, then they are parallel
to each other.
EX:
If p ll q and
q ll r
Then p ll r

3.12 In a plane, if 2 lines are
perpendicular to the same
line, then they are parallel to
each other.

EX:
4.1 Triangle Sum Theorem: the
sum of the measures of the
interior angles of a triangle is
180 degrees.
EX:
m<A + m<B + m<C = 180

4.2 Exterior Angle Theorem: The
measure of an exterior angle of
a triangle is equal to the sum of
the measures of the 2 non
adjacent interior angles.

EX: m<1 = m<A + m<B
4.3 Third Angle Theorem: If 2
angles of one triangle are
congruent to the 2 angles of
another triangle, then the third
angles are also congruent.
EX:
If m<A = m<D and A
m<B = m<E then
m<C = m<F
B

D
C
E
F
4.4 Reflexive Property of Congruent
Triangles: Every triangle is congruent to
itself
Symmetric Property of congruent triangles
examples
Transitive property of congruent triangles
examples
EX:
ABC =
ABC =
ABC =
ABC =
ABC
DEF, then
DEF, and
JKL
DEF =
DEF=
ABC
JKL, then
4.5 Angle-Angle-Side (AAS):
Congruence Theorem: If 2 angles
and a nonincluded side of 1
triangle are congruent to 2 angles
and the corresponding nonincluded
side of a second triangle, then the
2 triangles are congruent.
Angle m<A = m<D
 Angle m<B = m< E
 Side BC = EF
B

A
E
C D
F
4.6 Base Angles Theorem: If 2
sides of a triangle are
congruent, then the angles
opposite them are congruent.
If AB = CB, then m<A = m<C

B


A
C
4.7 Converse of the Base Angles
Theorem: If 2 angles of a
triangle are congruent, then the
sides opposite them are
congruent.

If m<A = m< C, then AB = CB

A
B
C
4.8 Hypotenuse-Leg (HL) congruence
theorem: If the hypotenuse and a leg of
a right triangle are congruent to the
hypotenuse and a leg of a second
triangle, then the 2 triangles are
congruent.
If BC = EF, and AC = DF, then
ABC =
DEF
A
***2 RIGHT TRIANGLES***
B
D
C
E
F
5.1 Perpendicular Bisector
Theorem: If a point is on a
perpendicular bisector of a
segment, then it is equidistant from
the end points of the segment.

If CP is a perpendicular bisector of AB,
then CA = CB
5.2 Converse of the Perpendicular
Bisector Theorem: If a point is
equidistant from the endpoints of a
segment, then it is on the
perpendicular bisector of the
segment.

If DA = DB, then D lies on the
perpendicular bisector of AB.
5.3 Angle Bisector Theorem: If a
point is on the bisector of an
angle, then it is equidistant from
the two sides of the angle.

If m<BAD = m<CAD, then DB = DC
5.4 Converse of the Angle Bisector
Theorem: If a point is in the interior
of an angle and is equidistant from
the sides of the angle, then it lies
on the bisector of the angle.

If DB = DC, then m<BAD = m<CAD
5.5 Concurrency if the
Perpendicular Bisectors of a
Triangle: The perpendicular
bisectors of a triangle intersect at a
point that is equidistant from the
vertices of the triangle.


PA = PB = PC
B
A
C
5.6 Concurrency of Angle Bisectors
of a Triangle: The angle bisectors
of a triangle intersect at a point that
is equidistant from the sides of the
triangle.





PD = PE = PF
B
F
A
D
P
E
C
5.7 Concurrency of the Medians of
a Triangle: The medians of a
triangle intersect at a point that is
two thirds of the distance from each
vertex to the midpoint of the
opposite side

If P is the centroid of triangle ABC, then
AP= 2/3 AD, BP= 2/3 BF,and CE= 2/3 CP
5.8 Concurrency of Altitudes of
a Triangle: The lies containing
the altitudes of a triangle are
congruent.

If AE, BF, and CF are the altitudes of
triangle ABC, then the lines AE, BF, and
CD intersect at some point.
5.9 Midsegment Theorem: The
segment connecting the
midpoints of two sides of a
triangle is parallel to the third
side and is half as long.

DE ll AB, and DE = ½ AB
5.10 If one side of a triangle is
longer than another side, then
the angle opposite the longer
side is larger than the angle
opposite the shorter side.
m<A > m<C
B
3
A
5
C
5.11 If one angle of a triangle is
larger than another angle, then
the side opposite the larger
angle is longer than the side
opposite the smaller angle.

EF > DF
5.12 Exterior Angle Inequality: The
measure of an exterior angle of
a triangle is greater than the
measure of either of the two
nonadjacent interior angles.
m<1 > m<A and m<1 > m<B
5.13 Triangle Inequality: The
sum of the lengths of any two
sides of a triangle is greater
than the length of the third side.
AB + BC > AC
AC + BC > AB
AB + AC > BC
A
C
B
5.14 Hinge Theorem: If two sides of one
triangle are congruent to two sides of
another triangle, and the included angle of
the first is larger than the included angle of
the second, then the third side of the first is
longer than the third side of the second

RT > VX
R
V


100 S
T
80 W
X
5.15 Converse of the Hinge Theorem: If two
sides of one triangle are congruent to two
sides of another triangle, and the third side
of the first is longer than the third side of the
second, then the included angle of the first is
larger than the included angle of the second.
m<A > m<D
B
A
E
D
C
F
6.1 Interior Angles of
Quadrilateral: The sum of the
measures of the interior angles
of a quadrilateral is 360.
m<1 + m<2 + m<3 + m<4 = 360 degrees
6.2 If a quadrilateral is a
parallelogram, then its opposite
sides are congruent



PQ = RS and SP = QR
Q
P
R
S
6.3 If a quadrilateral is a
parallelogram, then its opposite
angles are congruent.
m<P = m<R and m<Q = m<S
Q
R
P
S
6.4 If a quadrilateral is a
parallelogram, then its
consecutive angles are
supplementary.
m<P + m<Q = 180, m<Q + m<R = 180
M<R + m<S = 180, m<S + m<P = 180
Q
P
R
S
6.5 If a quadrilateral is a
parallelogram, then its
diagonals bisect each other
QM = SM and PM = RM
Q
R
P
S
6.6.
If both pairs of opposite
sides of a quadrilateral are
congruent, then the
quadrilateral is parallelogram.

ABCD is a parallelogram


A
B


C
D
6.7 If both pairs of opposite
angles of a quadrilateral are
congruent, then the
quadrilateral is a parallelogram.

ABCD is a parallelogram
A


C
B
D
6.8
If an angle of a
quadrilateral is supplementary
to both of its consecutive
angles, then the quadrilateral is
a parallelogram.
ABCD is a parallelogram

A

C

B
D
6.9
If the diagonals of a
quadrilateral bisect each other,
then the quadrilateral is
parallelogram.
ABCD is a parallelogram

A


C
B
D
6.10 If one pair of opposite sides of a quadrilateral
are congruent and parallel, then the quadrilateral is
a parallelogram.
Rhombus Corollary: A quadrilateral is a rhombus
if and only if it has four congruent sides.
Rectangle Corollary: A quadrilateral is a rectangle
if and only if it has four right angles.
Square Corollary: A quadrilateral is a square if
and only if it is a rhombus and a rectangle.
ABCD is a parallelogram
A
C
B
D
6.11 A parallelogram is a
rhombus if and only if its
diagonals are perpendicular.
ABCD is a rhombus iff AC perpendicular to
BD

B
C

A
D

6.12 A parallelogram is a
rhombus if and only if each
diagonal bisects a pair of
opposite angles.



ABCD is a rhombus iff AC bisects <DAB and <BCD and
BD bisects <ADC and <CBA
B
A
C
D
6.13 A parallelogram is a
rectangle if and only if its
diagonals are congruent.
ABCD is a rectangle iff AC = BD

A
B


C
D
6.14 If a trapezoid is isosceles,
then each pair of base angles is
congruent.
m<A = m<B, m<C =m<D
A
B
C
D
6.15 If a trapezoid has a pair of
congruent base angles, then it
is an isosceles trapezoid
ABCD is an isosceles trapezoid

A
B


C
D
6.16 A trapezoid is isosceles if
and only if its diagonals are
congruent.
ABCD is isosceles iff AC = BD
A
C
B
D
6.17 Midsegment Theorem for
Trapezoids: The midsegment of a
trapezoid is parallel to each base
and its length is one half the sum of
the lengths of the bases.
MN ll AD, MN ll BC, MN = ½ (AD + BC)
B
C
M
N
A
D
6.18 If quadrilateral is a kite,
then its diagonals are
perpendicular.
AC perpendicular BD
C
B
D
A
6.19 If a quadrilateral is a kite,
then exactly one pair of
opposite angles are congruent.
m<A = m<C, m<B is not equal m<D
C
B
D
A
6.20 Area of a Rectangle: The
area of a rectangle is the
product of its base and height.

A = bh
h



b
6.21 Area of a Parallelogram:
The area of a parallelogram is
the product of a base and its
corresponding height.



A = bh
h
b
6.22 Area of a Triangle: The
area of a triangle is one half
the product of a base and its
corresponding height.
A = ½ bh
h
b
6.23 Area of a Trapezoid: The
area of a trapezoid is one
half the product of the height
and the sum of the bases.
A = ½ h(b 1 + b 2 )
b1
h
b2
6.24 Area of a Kite: the area of
a kite is one half the product of
the lengths of its diagonals.
A = ½ d1 *d2
d1
d2
6.25 Area of a Rhombus: the
area of a rhombus is equal to
one half the product of the
lengths of diagonals.
A = ½ d1 *d2
d1
d2
7.1 Reflection Theorem: A
reflection is an isometry
Isometry is a transformation that preserves
lengths
line of reflection
7.2 Rotation Theorem: A rotation
is an isomentry.
Point of rotation
180 degree
rotation
7.3 Rotational theorem using
lines and coordinate planes
Rotational point
7.4 Translation Theorem: A
translation is an isometry.
P’


P
Q’


Q
7.5 Reflections
k



Q
P
m
Q’
P’
Q’’
P”
7.6 Composition Theorem: The
composition of two (or more)
isometrics is an isometry
When 2 or more transformations are
combined to produce a single
transformation
EX: reflection then translation
8.1 If two polygons are similar,
then the ratio of their perimeters
is equal to the ratios of their
corresponding side lengths.
Ratio perimeter = ratio of sides
K
L P
Q
N
M S
R
8.2 Side-Side-Side (SSS)
Similarity Theorem: If the
corresponding sides of two
triangles are proportional, then
the triangles are similar.
IF AB = BC = CA
PQ
QR RP’
Then
ABC ~ PQR
8.3 Side-Angle-Side (SAS) Similarity
Theorem: If an angle of one triangle is
congruent to an angle of a second
triangle and the lengths of the sides
including these angles are proportional,
then the triangles are similar.
If m<X = m<M and ZX = XY
PM MN’
Then
XYZ ~
MNP
8.4 Triangle Proportionally
Theorem: If a line parallel to one
side of a triangle intersects the
other two sides, then it divides
the two sides proportionally.
If TU ll QS, then RT = RU
TQ
US
8.5 Converse of the Triangle
Proportionally Theorem: If a line
divides two sides of a triangle
proportionally, then it is parallel
to the third side.
IF RT = RU, then TU ll QS
TQ
US
8.6 If three parallel lines
intersect two transversals, then
they divide the transversals
proportionally.
If r ll s and s ll t, and l and m intersect r, s,
and t, then UW = VX
WY XZ
8.7 If a ray bisects an angle of a
triangle, then it divides the opposite
side into segments whose lengths
are proportional to the lengths of
the other two sides.
If CD bisects <ACB, then
9.1 If an altitude is drawn to the
hypotenuse of a right triangle,
then the two triangles formed
are similar to the original
triangle and to each other.
9.2 In a right triangle, the altitude from the
right angle to the hypotenuse divides the
hypotenuse divides they hypotenuse into
two segments. The length of the altitude is
the geometric mean of the lengths of the two
segments.
9.3 In a right triangle, the altitude from the
right angle to the hypotenuse divides the
hypotenuse into two segments. Each leg of
the right triangle is the geometric mean of
the hypotenuse and the segment of the
hypotenuse that is adjacent to the leg.
9.4 Pythagorean Theorem: In a
right triangle, the square of the
length of the hypotenuse is
equal to the sum of the squares
of the lengths of the legs.
9.5 Converse of the Pythagorean
Theorem: If the square of the length of
the longest sides a triangle is equal to
the sum of the sum of the squares of
the lengths of the other two sides, then
the triangle is a right triangle.
9.6 If the square of the length of the
longest side of triangle is less than
the sum of the squares of the
lengths of the other two sides, then
the triangle is acute.
9.7 If the square of the length of the
longest side of a triangle is greater
than the sum of the squares of the
length of the other two sides, then
the triangle is obtuse.
9.8 45° -45 ° -90° Triangle
Theorem: In a 45° -45 ° -90°
triangle, the hypotenuse is √2
times as long as each leg.
9.9 30° -60° -90° Triangle Theorem:
In a 30° -60° -90° triangle, the
hypotenuse is twice as long as the
shorter leg, and the longer leg √3
times as long as the shorter leg.
10.1 If a line is tangent to a
circle, then it is perpendicular to
the radius drawn to the point of
tangency.
10.2 In a plane, if a line is
perpendicular to a radius of a
circle at its endpoint on the
circle, then the line is tangent to
the circle.
10.3 If two segments from the
same exterior point are tangent
to a circle, then they are
congruent.
10.4 In the same circle, or in
congruent circles, two minor
arcs are congruent if and only if
their corresponding chords are
congruent.
10.5 If a diameter of a circle is
perpendicular to a chord, then
the diameter bisects the chord
and its arc.
10.6 If one chord is a
perpendicular bisector of
another chord, then the first
chord is a diameter.
10.7 In the same circle or in
congruent circles, two chords
are congruent if and only if they
are equidistant from the center.
10.8 If an angle is inscribed in a
circle, then its measure is half
the measure of its intercepted
arc.
10.9 If two inscribed angles of a
circle intercept the same arc,
then the angles are congruent.
10.10 If a right triangle is inscribed in a
circle, then the hypotenuse is a diameter of
the circle. Conversely, if one of an inscribed
triangle is a diameter of the circle, then the
triangle is right triangle and the angle
opposite the diameter is the right angle.
10.11 A quadrilateral can be
inscribed in a circle if and only if
its opposite angles are
supplementary.
10.12 If a tangent and a chord
intersect at a point on a circle,
then the measure of each angle
formed is one half the measure
of its intercepted arc.
10.13 If two chords intersect in the
interior of a circle, then the
measure of each angle is one half
the sum of the measures of the
arcs intercepted by the angle and
its vertical angle.
10.14 If a tangent and a secant, two
tangents, or two secants intersect in
the exterior of a circle, then the
measure of the angle formed is one
half the difference of the measures of
the intercepted arcs.
10.15 If two chords intersect in the
interior of a circle, then the product of
the lengths of the segments of one
chord is equal to the product of the
lengths of the segments of the other
chord.
10.16 If two secant segments share the
same endpoint outside a circle, then the
product of the length of one secant segment
and the length of its external segments
equals the product of the length of the other
secant segment and the length of its
external segment.
10.17 If a secant segment and a tangent
segment share an endpoint outside a circle,
then the product of the length of the secant
segment and the length of its external
segment equals the square of the length of
the tangent segment.
11.1 Polygon Interior Angles
Theorem: The sum of the
measures of the interior angles
of a convex n-gon is (n-2) ∙
180°.
11.2 Polygon Exterior Angles Theorem: The
sum of the measures of the exterior angles
of a convex polygon, one angle at each
vertex, is 360°.
Corollary: The measure of each exterior
angle of regular n-gon is 1/n ∙ 360°, or
360°/n
11.3 Area of an Equilateral
Triangle: The area of an
equilateral triangle is one fourth
the square of the length of the
side times √3.
11.4 Area of a Regular Polygon:
The area of a regular n-gon with
side length s is half the product of
the apothem a and the perimeter P,
so A = ½ aP, or A = ½a ∙ ns.
11.5 Areas of Similar Polygons:
If two polygons are similar with
the lengths of corresponding
sides in the ratio of a:b, then the
ratio of their areas is a2:b2.
11.6 Circumference of a Circle: The
circumference C of a circle is C = pd or C =
2pr, where d is the diameter of the circle and
r is the radius of the circle. Arc Length
Corollary: In a circle, the ratio of the length
of a given arc to the circumference is equal
to the ratio of the measure of the arc to
360°.
11.7 Area of a Circle: The area
of a circle is p times the square
of the radius, or A = pr2.
11.8 Area of a Sector: The ratio of
the area A of a sector of a circle to
the area of the circle is equal to the
ratio of the measure of the
intercepted arc to 360°.
12.1 Euler’s Theorem: The
number of faces (F), vertices
(V), and the edges of a
polyhedron are related by the
formula F + V= E+2.
12.2 Surface Area of a Right Prism:
The surface area S of a right prism
can be found using the formula S =
2B+Ph where B is the area of a
base, P is the perimeter of a base,
and h is the height.
12.3 Surface Area of Right Cylinder: The
surface area S of a right cylinder is
S = 2B + Ch = 2pr2 + 2prh2, where B is the
area of a base, C is the circumference of a
base, r is the radius of a base and h is the
height.
12.4 Surface Area of a Regular Pyramid:
The surface area S of a regular pyramid is S
of a regular pyramid is S = B + ½ P l, where
B is the area of a base, P is the perimeter of
the base, and l is the slant height.
12.5 Surface Area of a Right
Cone: The surface area S of a
right cone S =pr2 +prl, where r
is the radius of the base and l is
the slant height.
12.6 Cavalieri’s Principle: IF two
solids have the same height and
the same cross- sectional area
at every level then they have
the same volume.
12.7 Volume of a Prism: The
volume V of a prism is V =Bh,
where B is the area of a base
and h is the height.
12.8 Volume of a Cylinder: The
volume of V of a cylinder is V =
Bh = pr2h, where B is the area
of a base, and h is the height,
and r is the radius of a base.
12.9 Volume of a Pyramid: The
volume V of a pyramid is V =
1/3Bh, where B is the area of a
base, h is the height.
12.10 Volume of a Cone: The
volume V of a cone is V = 1/3Bh
= 1/3pr2h, where B is the area
of the base, h is the height, and
r is the radius of the base.
12.11 Surface Area of a Sphere:
The surface area S of a sphere
with radius r is S = 4pr2.
12.12 Volume of a Sphere: The
volume V of a sphere with the
radius r is V = 4/3pr3.
12.13 Similar Solids Theorem: If
two similar solids have a scale
factor of a:b, then corresponding
areas have a ratio of a2:b2, and
corresponding volumes have a
ratio of a3:b3.