# Db bisects adc help!!

• Dec 2nd 2013, 03:58 AM
Fentonjc
Db bisects adc help!!
Help I am totally lost. I have to do a proof problem with the statement and reason and I just don't get it.

Given: DB bisects /ADC
Prove: DB ' AC
• Dec 2nd 2013, 04:26 AM
Melody2
Re: Db bisects adc help!!
Quote:

Originally Posted by Fentonjc
Help I am totally lost. I have to do a proof problem with the statement and reason and I just don't get it.

Given: DB bisects /ADC
Prove: DB ' AC

I am going to demonstrate my lack of knowledge immediately by asking you to explain what the symbols mean. Please.
That is /ADC what is the forward slash
and
what is the apostrophy.
• Dec 2nd 2013, 04:55 AM
Melody2
Re: Db bisects adc help!!
Quote:

Originally Posted by Fentonjc

Given: DB bisects /ADC
Prove: DB ' AC

Hi Fentonjc,

I am going to assume that /ADC means angle ADC
and DB ' AC means DB bisects AC (the only other alternative that I can think of is that DB is perpendicular to AC and the proof would be similar)

Draw the picture first of course
Let X be the intersection of DB and AC

Consider triangle ADX and triangle CDX

you can prove that these 2 triangles are congruent and hence show that AX=CX
then give a concluding statement and you are finished.

Is that enough help?
Melody.
• Dec 2nd 2013, 07:00 AM
Soroban
Re: Db bisects adc help!!
Hello, Fentonjc!

I am getting better at Mathematical Forensics.
I think I understand the problem . . .

Quote:

$\text{Given: }\:\text{Triangle }ADC.$
. . . . . . $DB\text{ bisects }\angle ADC.$
. . . . . . $AD = CD$
$\text{Prove: }\:DB \perp AC$

Code:

              D               *             /|\             / | \           /  |  \           /  |  \         /    |    \         /    |    \       /      |      \     A * - - - * - - - * C               B
We are given: . $AD = CD.$

We are told that $DB$ bisects $\angle ADC.$
Then: . $\angle BDA = \angle BDC$

Also: . $DB =DB$ (Identity)

So: . $\Delta DBA \cong \Delta DBC$ (s.a.s.)

Hence: . $\angle DBA = \angle DBC$ (corresponding parts)

We see: . $\angle DBA + \angle DBC \,=\,180^o$

Since $\angle DBA = \angle DBC,\;\angle DBA = 90^o$

Therefore: . $DB \perp AC.$
• Dec 2nd 2013, 05:09 PM
Fentonjc
Re: Db bisects adc help!!
I tried to attach the actual picture. Then it has a box that has 2 sides ones says statements and the other says reasons.

it is a triangle that has a D on top and A B C on the bottom and it also has a 1 and 2 inside the triangle under the D
• Dec 2nd 2013, 06:17 PM
Melody2
Re: Db bisects adc help!!
There you go Soroban. You are good at Forensic mathematics! You even had the diagram around the right way.
I'm impressed.

I have a soroban. It was given to me by a Japanese exchange student. It was a great gift!