Transcript Chapter 3
Chapter Three
Building Geometry Solid
Incidence Axioms
I-1:
For every point P and for every
point Q not equal to P there exists a
unique line l incident with P and Q.
I-2: For every line l there exist at least
two distinct points that are incident with l.
I-3: There exist three distinct points
with the property that no line is incident
with all three of them.
Betweenness Axioms (1)
B-1 If A*B*C, then A,B,and C are three distinct points
all lying on the same line, and C*B*A.
B-2: Given any two distinct points B and D, there
exist points A, C, and E lying on BD such that A
* B * D, B * C * D, and B * D * E.
B-3: If A, B, and C are three distinct points lying
on the same line, then one and only one of the points
is between the other two.
P-3.1: For any two points A and B:
i. AB BA AB and ii. AB BA {AB}
Def: Let l be any line, A and B any points
that do not lie on l. If A = B or if segment
AB contains no point lying on l, we say A
and Be are on the same sides of l.
Def: If A B and segment AB does
intersect l, we say that A and B are opposite
sides of l.
Betweenness Axioms (2)
B-4: For every line l and for any three points A,
B, and C not lying on l:
(i)
If A and B are on the same side of l
and B and C are on the same side of l, then A
and C are on the same side of l.
(ii) If A and B are on opposite sides of l
and B and C are on opposite sides of l, then A
and C are on the same side of l.
Corollary (iii) If A and B are on opposite sides of l
and B and C are on the same side of l, then A and
C are on opposite sides of l.
P-3.2: Every line bounds exactly two halfplanes and these half-planes have no point in
common.
P-3.3: Given A*B*C and A*C*D. Then
B*C*D and A*B*D.
Corollary: Given A*B*C and B*C*D. Then
A*B*D and A*C*D.
P-3.4: Line Separation Property: If C*A*B
and l is the line through A, B, and C (B-1),
then for every point P lying on l, P lies
either on ray AB or on the opposite ray AC .
AB
Pasch’s Theorem
If A, B, C are distinct noncollinear points and
l is any line intersecting AB in a point
between A and B, then l also intersects
either AC or BC. If C does not lie on l, then
l does not interesect both AC and BC.
Def: Interior of an angle. Given an angle
CAB, define a point D to be in the interior of
CAB if D is on the same side of AC as B and
if D is also on the same side of AB as C.
P-3.5: Given A*B*C. Then AC = ABBC and
B is the only point common to segments AB and
BC.
P-3.6: Given A*B*C. Then B is the only point
common to rays BA and B C , and AB AC.
P-3.7: Given an angle CAB and point D lying
on line BC . Then D is in the interior of CAB
iff B*D*C.
P3.8: If D is in the interior of CAB; then:
a) so is every other point on ray AD
except A;
b) no point on the opposite ray to AD is in
the interior of CAB; and
c) if C*A*E, then B is in the interior of
DAE.
Crossbar Thm: If AD is between AC
and AB , then AD intersects segment BC.
A ray AD is between rays A C and A B if A B
and A C are not opposite rays and D is
interior to CAB.
The interior of a triangle is the intersection
of the interiors of its three angles.
P-3.9: (a) If a ray r emanating from an ex-
terior point of ABC intersects side AB in a
point between A and B, then r also intersects
side AC or side BC.
(b) If a ray emanates from an interior
point of ABC, then it intersects one of the
sides, and if it does not pass through a vertex, it
intersects only one side.
.
Congruence Axioms
C-1: If A and B are distinct points and if A' is
any point, then for each ray r emana-ting from A'
there is a unique point B' on r such that B' = A'
and AB A'B'.
C-2: If AB CD and AB EF, then CD EF.
Moreover, every segment is congruent to itself.
C-3: If A*B*C, A'*B'*C', AB A'B', and BC
B'C', then AC A'C'.
C-4: Given any angle BAC (where by definition of "angle” AB is not opposite to AC ), and
given any ray A' B' emanating from a point A’,
then there is a unique ray A' C' on a given side of
line A'B' such that B'A'C' = BAC.
C-5: If A B and A C, then
B C. Moreover, every angle is con-
gruent to itself.
C-6: (SAS). If two sides and the included
angle of one triangle are congruent respectively to two sides and the included angle of
another triangle, then the two triangles are
congruent.
Cor. to SAS: Given ABC and segment
DE AB, there is a unique point F on a given
side of line DEsuch that ABC DEF.
Propositions 3.10 - 12
P3.10: If in ABC
we have AB AC,
then B C.
P3.11: (Segment Substitution): If A*B*C,
D*E*F, AB DE, and AC DF, then BC
EF.
P3.12: Given AC DF, then for any point
B between A and C, there is a unique point
E between D and F such that AB DE.
Definition:
AB < CD (or CD > AB) means that there
exists a point E between C and D such that
AB CE.
Propositions 3.13
P3.13: (Segment Ordering):
(a) (Trichotomy): Exactly one of
the following conditions holds:
AB < CD, AB CD, or AC > CD;
(b) If AB < CD and CD EF,
then AB < EF;
(c) If AB > CD and CD EF,
then AB > EF;
(d) (Transitivity): If AB < CD
and CD < EF, then AB < EF.
Propositions 3.14 - 16
P3.14:
Supplements of congruent
angles are congruent.
P3.15: (a) Vertical angles are
congruent to each other.
(b) An angle congruent to a
right angle is a right angle.
P3.16: For every line l and every point
P there exists a line through P perpendicular to l.
Propositions 3.17 - 19
P3.17: (ASA Criterion for Congruence):
Given ABC and DEF with A D, C F,
and AC DF. Then ABC DEF.
P3.18: If in ABC we have B C, then AB
AC and ABC is isosceles.
P3.19: (Angle Addition): Given between
and , between and , CBG FEH, and GBA
HED. Then ABC DEF.
Proposition 3.20
P3.20: (Angle Subtraction): Given
between and , between and , CBG FEH,
and ABC DEF. Then GBA HED.
Definition:
ABC < DEF means there is a ray between
and such that ABC GEF.
Proposition 3.21 Ordering Angles
P3.21: (Ordering of Angles):
(a) (trichotomy): Exactly one of the
following conditions holds:
P < Q, P Q, P > Q (Q < P);
(b) If P < Q, and Q R, then P < R;
(c) If P > Q, and Q R, then P > R;
(d) If P < Q, and Q < R, then P < R.
Propositions 3.22 - 23
P3.22: (SSS Criterion for Congruence):
Given ABC and DEF. If AB DE,
and BC EF, and AC DF, then ABC
DEF.
P3.23: (Euclid's 4th Postulate): All right
angles are congruent to each other.