2. When we talk about congruent triangles,
we mean everything about them Is congruent.
All 3 pairs of corresponding angles are equal….
And all 3 pairs of corresponding sides are equal
3. For us to prove that 2 people are
identical twins, we don’t need to show
that all “2000” body parts are equal. We
can take a short cut and show 3 or 4
things are equal such as their face, age
and height. If these are the same I think
we can agree they are twins. The same
is true for triangles. We don’t need to
prove all 6 corresponding parts are
congruent. We have 5 short cuts or
methods.
4. SSS
If we can show all 3 pairs of corr.
sides are congruent, the triangles
have to be congruent.
5. SAS
Show 2 pairs of sides and the
included angles are congruent and
the triangles have to be congruent.
Included
angle
Non-included
angles
6. This is called a common side.
It is a side for both triangles.
We’ll use the reflexive property.
10. ASA, AAS and HL
A
ASA – 2 angles
and the included side
AAS – 2 angles and
The non-included side
S
A
A
A
S
11. HL ( hypotenuse leg ) is used
only with right triangles, BUT,
not all right triangles.
HL
ASA
12. When Starting A Proof, Make The
Marks On The Diagram Indicating
The Congruent Parts. Use The Given
Info, Properties, Definitions, Etc.
We’ll Call Any Given Info That Does
Not Specifically State Congruency
Or Equality A PREREQUISITE
13. SOME REASONS WE’LL BE USING
•
•
•
•
•
•
DEF OF MIDPOINT
DEF OF A BISECTOR
VERT ANGLES ARE CONGRUENT
DEF OF PERPENDICULAR BISECTOR
REFLEXIVE PROPERTY (COMMON SIDE)
PARALLEL LINES ….. ALT INT ANGLES
14. A
C
B
1 2
E
SAS
Given: AB = BD
EB = BC
Prove: ∆ABE = ∆DBC
˜
Our Outline
P rerequisites
D S ides
A ngles
S ides
Triangles =
˜
16. C
12
Given: CX bisects ACB
A= B
˜
Prove: ∆ACX = ∆BCX
˜
AAS
A
X
B
P CX bisects ACB
A
1= 2
A
A= B
S
CX = CX
∆’s ∆ACX = ∆BCX
˜
Given
Def of angle bisc
Given
Reflexive Prop
AAS