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Math Help - calculate perpendicular height of random triangle

  1. #1
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    Question calculate perpendicular height of random triangle

    how can i calculate the perpendicular height of random triangle where i have the 3 points (x+y) for the corners + also the angles for each corner?

    ideally i need to know how to calculate the area of any triangle using just the properties above, but how to calculate perpendicular height will do.

    thanks for your help
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  2. #2
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    Quote Originally Posted by .paul. View Post
    how can i calculate the perpendicular height of random triangle where i have the 3 points (x+y) for the corners + also the angles for each corner?

    ideally i need to know how to calculate the area of any triangle using just the properties above, but how to calculate perpendicular height will do.

    thanks for your help
    If the 3 corners are given by: P_1(x_1 , y_1)\ ,\ P_2(x_2 , y_2)\ ,\ P_3(x_3 , y_3) then the area of the triangle can be calculated by:

    A=\dfrac12\left(x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2) \right) = \dfrac12 \cdot \left|\begin{array}{ccc} x_1&y_1&1 \\ x_2&y_2&1 \\ x_3&y_3&1 \end{array} \right|
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    Question

    that works great with pixels, but i need to convert the output to cm squared.
    heres how i convert a pixel line length to cm:

    (pixels / gr.DpiX) * 2.54 where gr.DpiX is dots per inch in the graphics object.

    but that doesn't convert pixels squared to cm squared.
    any ideas?

    thanks again
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  4. #4
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    Quote Originally Posted by .paul. View Post
    that works great with pixels, but i need to convert the output to cm squared.
    heres how i convert a pixel line length to cm:

    (pixels / gr.DpiX) * 2.54 where gr.DpiX is dots per inch in the graphics object.

    but that doesn't convert pixels squared to cm squared.
    any ideas?

    thanks again
    The questin you originally posted has been answered. But it looks like the question you posted is not the question you wanted answered. In which case, it might help if you posted what the actual question is.
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    Quote Originally Posted by mr fantastic View Post
    The questin you originally posted has been answered. But it looks like the question you posted is not the question you wanted answered. In which case, it might help if you posted what the actual question is.
    that is the full question, in the 2 posts
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    Quote Originally Posted by .paul. View Post
    that is the full question, in the 2 posts
    1. It would save time and effort if the actual full question had been posted in your first post.

    2. Post #3 does not shed complete light on what the full and actual question is.
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  7. #7
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    Quote Originally Posted by .paul. View Post
    that works great with pixels, but i need to convert the output to cm squared.
    heres how i convert a pixel line length to cm:

    (pixels / gr.DpiX) * 2.54 where gr.DpiX is dots per inch in the graphics object.

    but that doesn't convert pixels squared to cm squared.
    any ideas?

    thanks again
    Just convert the pixel coordinates to cm, then apply the method given, and the answer will be in square centimetres.

    CB
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