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Vichien Lindsey
08-25-2005, 03:20 PM
Prove: if an isosceles triangle has an altitude from the vertex to the base, then the altitude bisects the vertex angle.
Given: angle ABC is isosceles; line CD is the altitude to base line AB
To Prove: line CD bisects angle C

Plan: _______?

Proof:
__________________________________________________ __________
Statements / Reasons


the triangle looks kinda like this c

Please help if u can, thanks

a---d---b [/img]

Gene
08-25-2005, 04:12 PM
Does this do it?

C
/|\
/ | \
A__D__B

AC = BC
AC˛= CD˛+AD˛
AC˛-CD˛=AD˛
BC˛-CD˛=BD˛=AC˛-CD˛
AD˛=BD˛
AD=BD
Congruant triangles by SSS.
I hope the reasons are obvious and legit.

Euler
08-25-2005, 04:35 PM
I'd suggest renting Euclid's Elements, if you are doing a section on proofs. He is like — Proofs incarnate. I would use him as an example.