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Math Help - Triangles!!! acute, obtuse, or right???

  1. #1
    Junior Member whytechocolate01's Avatar
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    Question Triangles!!! acute, obtuse, or right???

    State whether a triangle formed with sides having the lengths named is acute, right, or obtuse.

    3,4,6

    9,12,15

    5,6,7

    How the heck can I solve this? Please explain!
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  2. #2
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    Quote Originally Posted by whytechocolate01 View Post
    State whether a triangle formed with sides having the lengths named is acute, right, or obtuse.

    3,4,6

    9,12,15

    5,6,7

    How the heck can I solve this? Please explain!
    Use the law of cosines or Heron's formula.

    Let us use law of cosines, because you have a better chance of hearing of it.

    #1] Let a=3 b=4 and c=6.
    Then, we can find all the angles of this triangle.
    Say angle A.
    a^2=b^2+c^2-2bc*cos(A)
    9=16+36-48*cos(A)
    You can solve for cos(A) and then take arccos to get the angle.
    Now do that will all angles.
    Then you can determine whether the triangle if acute or not.
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