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Math Help - vector projection

  1. #1
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    vector projection

    [quote]Let T be the triangle with vertices at (4,10), (−8,8),(3,8). The area of T is = ? [quote]

    i used the projection forumla and got the length of 1 side as: 4.2426 (not sure if that is right). should i do the same thing to find the other sides?
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  2. #2
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    [QUOTE=viet;98972][quote]Let T be the triangle with vertices at (4,10), (−8,8),(3,8). The area of T is = ?

    i used the projection forumla and got the length of 1 side as: 4.2426 (not sure if that is right). should i do the same thing to find the other sides?
    You can get the area of the triangle directly using Heron's formula.

    -Dan
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  3. #3
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    It is really easy we recall a basic formula:
    A = \frac{1}{2}a \cdot b\sin \left( \phi  \right) = \frac{1}{2}\left\| {a \times b} \right\|.
    That is one-half the dot product of the two vectors forming two sides of the triangle times the sine of the angle between. But sine is related to the cross product.
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