Results 1 to 6 of 6

Math Help - Surds (length of a side of a rhombus)

  1. #1
    Junior Member
    Joined
    Apr 2010
    Posts
    42

    Surds (length of a side of a rhombus)



    I tried Pythagora's theorem and I think I'm close to the answer, but I'm stuck at this point:

    Sorry for the images, Latex is kind of confusing for me :s

    Any help would be greatly appreciated and thank you in advance.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member Bacterius's Avatar
    Joined
    Nov 2009
    From
    Wellington
    Posts
    927
    Hello !

    You are close to the answer. You have the same one, written in a different form, but you need some more work to get to their actual answer :

    BC^2 = 18 \frac{4}{5} + 4 \sqrt{5} - \frac{12}{\sqrt{5}}

    First, we need to put everything in absolute fraction form (otherwise things get confusing) :

    BC^2 = \frac{94}{5} + 4 \sqrt{5} - \frac{12}{\sqrt{5}}

    Note that you can multiply everything by 5 :

    5 BC^2 = 94 + 20 \sqrt{5} - 12 \sqrt{5}

    Then you can factor a 2 out :

    5 BC^2 = 2 \left (47 + 10 \sqrt{5} - 6 \sqrt{5} \right )

    Simplifying the surds :

    5 BC^2 = 2 \left (47 + 4 \sqrt{5} \right )

    And finally, dividing by 5 :

    BC^2 = \frac{2}{5} \left (47 + 4 \sqrt{5} \right )

    Does it make sense ?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Apr 2010
    Posts
    42
    Thank you very much!
    If I use my original answer ( BC^2 = 18\frac{4}{5} + 4\sqrt5 - \frac{12}{\sqrt5} ) is it still considered to be a correct answer if I use it in, say, a test? Or would it be incorrect because it is not fully simplified?
    Thanks.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member Bacterius's Avatar
    Joined
    Nov 2009
    From
    Wellington
    Posts
    927
    Quote Originally Posted by caramelcake View Post
    Thank you very much!
    If I use my original answer ( BC^2 = 18\frac{4}{5} + 4\sqrt5 - \frac{12}{\sqrt5} ) is it still considered to be a correct answer if I use it in, say, a test? Or would it be incorrect because it is not fully simplified?
    Thanks.
    I believe you might lose some points depending on the context, but it wouldn't be penalized that much unless the question specifically asks for full simplification/factorization. But if you can factorize, do it (here there were two identical surds which sort of looks bad)
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Apr 2010
    Posts
    42
    OK, thanks a lot for your input!
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Super Member Bacterius's Avatar
    Joined
    Nov 2009
    From
    Wellington
    Posts
    927
    It was my pleasure.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 6
    Last Post: August 17th 2011, 05:42 AM
  2. Replies: 2
    Last Post: June 25th 2011, 01:21 PM
  3. Replies: 2
    Last Post: October 18th 2010, 05:32 AM
  4. Diagonal and Side of a Rhombus
    Posted in the Geometry Forum
    Replies: 1
    Last Post: May 19th 2009, 05:37 PM
  5. Length of Side b
    Posted in the Geometry Forum
    Replies: 2
    Last Post: January 5th 2009, 10:58 PM

Search Tags


/mathhelpforum @mathhelpforum