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Math Help - SA of a regular tetrahedron

  1. #1
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    SA of a regular tetrahedron

    A regular tetrahedron is a triangular
    pyramid. What is the total surface
    area of a regular tetrahedron with
    base edges of 7 cm?

    I started by using
    1/2 Perimeter [Side Length] + [Base Area]
    (1/2) (21) (?) + (sqrt(36.75))

    So im not sure if this is the correct forumula or if the numbers i used to plug in are correct.
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  2. #2
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    Opalg's Avatar
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    The tetrahedron has four faces, each of which is an equilateral triangle with sides 7 cm. So your answer should be 4 times the area of that triangle.

    The area of the triangle is half the base, times the vertical height which in this case is 7\sin60^\circ = 7\sqrt3/2.

    Put all that information together and you'll get the answer.
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