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Finding a side length in similar triangles?

  1. Feb 6, 2012 #1
    Side note: PF is awesome! This is kind of like Tutor.com, only it's free and others can contribute their answers.

    1. The problem statement, all variables and given/known data
    Explain why triangle ABD is similar to triangle ABC and then find the length of side AB. Angles B and C are congruent. m(ADB)+m(BDC) = 180 degrees. AD=4 and DC=12.

    2. Relevant theorems, postulates, properties, etc.
    Corresponding parts of similar angles are similar.
    Symmetric property of similarity - if XYZ is similar to ABC, then XZY is similar to ACB, ZXY is similar to CAB, etc.

    3. The attempt at a solution
    The similarity ratio is 4:16 (side length in ABD:side length in ABC).I know that. If I knew at least one side length I could easily figure out what AB is. The problem is I don't.
  2. jcsd
  3. Feb 6, 2012 #2


    Staff: Mentor

    It would be helpful if you could post a screen shot or sketch of the two triangles.
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