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Math Help - Db bisects adc help!!

  1. #1
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    Question 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
    AD congruent CD
    Prove: DB ' AC
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  2. #2
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    Re: Db bisects adc help!!

    Quote Originally Posted by Fentonjc View Post
    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
    AD congruent CD
    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.
    Thanks from emakarov and topsquark
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  3. #3
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    Re: Db bisects adc help!!

    Quote Originally Posted by Fentonjc View Post

    Given: DB bisects /ADC
    AD congruent CD
    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.
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  4. #4
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    Re: Db bisects adc help!!

    Hello, Fentonjc!

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


    \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.
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    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
    Attached Thumbnails Attached Thumbnails Db bisects adc help!!-mat207-week-3-proof-problem.jpg  
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  6. #6
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    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!
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