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Math Help - Proving Triangles Similar! Application problem

  1. #1
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    Proving Triangles Similar! Application problem

    Hey Guys,

    For #25)

    I am dealing with proportionals here with this problem and I don't know how to get the answer to this one.

    I tried 10/8 = 4/x

    AC/DE = AD/DB

    I ended up getting x = 3.2 but the answer is 16 .



    I have an idea that will get me 16 but... I honestly don't know if it's right

    so I set up the equation as 10/4 = x/8 which gets me x =20
    then I plug in 20 into x because DB = AB - AD and I get 20-4 = 16

    But if I plug in numbers like this, I don't understand why I should set it up as AC / AD = DE / DB.
    Attached Thumbnails Attached Thumbnails Proving Triangles Similar! Application problem-screen-shot-2013-11-04-11.22.00-pm.png  
    Last edited by Cake; November 4th 2013 at 10:33 PM.
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  2. #2
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    Re: Proving Triangles Similar! Application problem

    Hey Cake.

    With similarity you have AB/DB = AC/DE but AB = AD + DB which means

    (AD + DB)/DB = AC/DE which implies
    AD + DB = AC*DB/DE which imlies
    DB(AC/DE - 1) = AD which implies
    DB = AD / [AC/DE - 1] if my working out is correct.
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  3. #3
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    Re: Proving Triangles Similar! Application problem

    Quote Originally Posted by Cake View Post
    Hey Guys,

    For #25)

    I am dealing with proportionals here with this problem and I don't know how to get the answer to this one.

    I tried 10/8 = 4/x

    AC/DE = AD/DB

    I ended up getting x = 3.2 but the answer is 16 .



    I have an idea that will get me 16 but... I honestly don't know if it's right

    so I set up the equation as 10/4 = x/8 which gets me x =20
    then I plug in 20 into x because DB = AB - AD and I get 20-4 = 16

    But if I plug in numbers like this, I don't understand why I should set it up as AC / AD = DE / DB.

    Let DB =x
    x/x+4 = 8/10
    Thanks from LimpSpider and Cake
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  4. #4
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    Re: Proving Triangles Similar! Application problem

    Triangles ABC and ADE are similar thus we have
    BD/AB = DE/AC
    BD/( BD + AD) = 8/10
    10 * BD = ( BD + 4) * 8
    10 BD = 8 BD + 32
    That gives BD = 16
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  5. #5
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    Re: Proving Triangles Similar! Application problem

    Thank you guys!
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