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A good handyman ^^

A man called January is a clumsy handyman (like Baptiste), so one day he wants to make a right-angled triangle table. With his ruler he measures two sides of a piece of wood, but then his ruler breaks. Therefore he tries to measure the angles with a protractor; but after measuring the first angle his protractor breaks too (he has very bad luck).
With the measures help Mr. January to verify if his table is a right-angled triangle.

Mr. January knows that:

  • CB = 50 cm
  • AB = 60 cm
  • CBA = 39°

Posted in Group 8.


6 Responses

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  1. Lisbeth says

    Hi

    It is a good exercise but we are having trouble reading the letters and numbers on the triangle on the drawing of it.
    And it seems that you have named the sides wrong according to the information you give us.

    Looking forward to hear from you again!

  2. Baptiste says

    Hi,

    There are mistakes ^^, the informations are :
    – CA = 50 cm
    – AB = 60 cm
    – CBA = 39°
    You can see the triangle at : http://blogpeda.ac-poitiers.fr/lp2i/files/2008/04/problem1.png

  3. Sofie says

    We will say that it is not a right-angled triangle because:

    A= cos^-1 ((50^2 + c^2 – 60^2) / (2 * 50 * c)) = cos^-1 ((50^2 + 78,1^2 – 60^2) / (2 * 50 * 78,1)) = 50,2 degrees!

    If it was a right-angled triangle would our result be 90 degrees!

  4. Baptiste says

    I can’t accept your answer :

    If I understand all your answer you apply cos^-1 to the angle A, you can’t because it is maybe the right-angle. And the angle C is not about 78,1°.

    There are lot of ways to resolve this problem !

    I think you can try again, if it is me who don’t understand your answer, can you explain more ?

  5. Lisbeth says

    We try again in another way. ´
    The angle C is: C=sin^-1 ( ( 60 * sin(39) ) / 50) = 49,04 degrees.
    The angle A is: 180 – 39 – 49,04 = 91,96 degrees.

    The angle is not excactly right angled but Mr. January is very close.

  6. Baptiste says

    Okay, this is the good answers !! (In reality this is the only way ^^)

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