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Homework Help: Urgent: Basic Trigonometry

  1. Jul 22, 2012 #1
    Hello Guys

    could you please help me to find the hypotenuse for the red triangle please.


    Attached Files:

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  2. jcsd
  3. Jul 22, 2012 #2


    Staff: Mentor

    you have a 3-4-5 right triangle the hyp is bisected

    with a little thought you have the answer before you
  4. Jul 22, 2012 #3
    thanks jedishrfu for your reply but can you explain to me more, because i did't understand what did you mean pls.

  5. Jul 22, 2012 #4
    First use the Pythagorean theorem to solve for the hypotenuse of the left triangle, you will get the ratios of all the sides you need and solving for (??) will be a simple algebra problem.
  6. Jul 22, 2012 #5


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    There is NO red triangle. What you have in red is a trapezoid. Do you mean the triangle all the way up to the vertex of the large triangle? If so, you know that its legs have length 3 and 4 and you can find the length of the hypotenuse using the Pythagorean theorem. If you actually mean the length of the red section as shown, you will need more information. jedishrfu is assuming that the red goes half way up the small triangle but I don't see any reason to assume that.

    By the way- with the lengths as given, the angle can't be exactly 40 degrees, though it is pretty close- about 38.6 degrees.
  7. Jul 22, 2012 #6
    Is it possible that the large triangle isn't a right triangle?

    There is nothing that I see to indicate that it has to be.
  8. Jul 22, 2012 #7


    Staff: Mentor

    yes, good point. why mention theta=40 and not show the right angle? This is another one of those "don't trust the diagram" problems. I retract my original suggestion, I was fooled by the apparent 3-4-5 triangle.
  9. Jul 22, 2012 #8
    the angle i assumed it, not real value. Got it? please help guy

  10. Jul 22, 2012 #9


    Staff: Mentor

    if you're saying its a rt triangle then you have the answer from my original post
  11. Jul 22, 2012 #10


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    Not unless you know how far up the little triangle the red goes.
  12. Jul 22, 2012 #11


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    Staff Emeritus
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    Here's that image displayed directly:

    There's a red trapezoid, but as HallsofIvy said, there's no red triangle !
  13. Jul 23, 2012 #12
    I feel like the diagram doesn't have nearly enough clarity to answer this question.

    Are the sides of the quadralateral in the bottom right of the triangle perpindicular to the sides of the triangle, or is the quad a parallelgram?
  14. Jul 23, 2012 #13
    yes Villyer , the quadrilateral is perpendicular to the sides of the triangle.

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