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Math Help - New to Geometry

  1. #1
    Newbie
    Joined
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    Whittier, Ca
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    Solve this proof

    Need some help to make sure that I am doing this correctly.

    PQ=QR ProvePR=QS ◄--------P-------Q----R--------S--------►


    Statements Reasons
    PQ=RS Given
    Q is between PR midpoint
    R is between QS midpoint
    PQ=QR
    QR=RS
    PQ+QR=QR+RS Segment Addition Postulate (Postulate 1.13)
    PR=PQ+QR and QS=QR+QS Segment Addition Postulate (Postulate 1.13)
    PR=QS Substitution Law (Postulate 1.11)

    Am I even on the right track?

    Sandy
    Last edited by sandyorn; March 12th 2013 at 06:31 PM.
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  2. #2
    Senior Member
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    Re: New to Geometry

    yes
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  3. #3
    MHF Contributor

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    Re: New to Geometry

    If your statement of the hypotheses is correct, just "PR= QR", is correct, you can't prove "PR= QS", it isn't necessarily so! Nothing is said about "S" so it could be anywhere. For example supose the distance from P to Q and from Q to R is "1" Then the distance from P to R is 2 but we can choose S to make the distance from Q to S to be anything we like.

    You say "Q is between PR" which makes no sense- PR is a number. What you want to say is that Q is between P and R. Same criticism of the next line but with the added point that there is nothing in your hypothesis that says that R is the midpoint of QS. Did your hypotheses include "QR= RS"? If so you had better add that!

    You say "PQ= QR" and "given" which is correct. But you don't need to say later "QP= QR" (and you should never have "Reasons" left blank!).
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