Honors Geometry 18 Nov 2011
EMPTY folders- put papers in your binders. ONLY keep weekly
warm up sheet and current day’s classwork in folders.
Warm-up- silently please 
what did you learn this week?
what was easy?
what is still confusing?
how can I help?
Objective
Students will write flow chart proofs.
Students will take notes, participate in class
discussion, do proofs and present to the class.
Homework due today
pg.
: 21, 22, 23
Homework due Tuesday, Nov. 22
pg. 239: 1- 4, 10 - 13
If two triangles
are back to back –
they share a
common SIDE
“same side”
A
B
AB CD
C
If two triangles meet at
a vertex– vertical
angles are congruent
D
If two triangles meet at a
vertex– and the sides are
parallel – look for alternate
interior angles
750
a
a
a
CPCTC…
If two triangles are congruent, then
Corresponding Parts of those Congruent Triangles are
Congruent CPCTC
You must make sure you have
CORRESPONDING PARTS SAME RELATIVE POSITION!!!
HINTS– Use colored pencils to mark corresponding parts.
Mark all info you know on the figure.
Redraw triangles separately.
Extend lines or draw additional lines to
make triangles.
Use ARROWS.
A proof is a written account of the complete
thought process that is used to reach a conclusion.
Each step of the process is supported by a theorem,
postulate or definition verifying why the step is possible.
In formal Euclidean proofs, no steps can be left out.
WHY????
“A proof is an argument, a justification, a reason
that something is true. It’s got to be a particular
kind of reasoning – logical – to be called a
proof….A proof is just the answer to the
question “Why?”, when the person asking the
question wants an argument that is
indisputable… “
retrieved Nov. 17, 2011 from http://www.math.sc.edu/~cooper/proofs.pdf
Proofs– HOW?
See page 237- 238
See example A- paragraph proof
flowchart proof
You can also do two column proofs.
1. Restate given information clearly.
Mark the information on a sketch.
2. State what you are trying to show.
3. Write the given information on the left.
Write what you are trying to show on the right.
4. Fill in the other boxes working backwards
and forwards as needed.
ASK:
what do I need to know in order to claim the conclusion
is true?
what must I show to prove the intermediate result?
a
practice
Do problems on handout 4.7
Be ready to share your work with the class.
debrief
what did you learn?
what is still confusing?