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Math Help - 3D trig

  1. #1
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    3D trig

    Help me with this question please

    http://i667.photobucket.com/albums/v...0001/wedge.jpg

    Thank you in advance
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  2. #2
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    Hello anonymous_maths
    Quote Originally Posted by anonymous_maths View Post
    Help me with this question please

    http://i667.photobucket.com/albums/v...0001/wedge.jpg

    Thank you in advance
    I'm assuming that all the angles at B and C are right-angles.

    Then, in the diagram I've attached, N is the required point on FE; P is the foot of the perpendicular from N to the base; and the required angle, a = \angle NDP.

    Then, from \triangle NDP,\, \tan a = \frac{NP}{DP}= \frac{6}{DP}

    \Rightarrow DP = \frac{6}{\tan a}

    Note now that FN = CP, and then consider \triangle DPC. By Pythagoras' Theorem: CP^2 = DP^2 - DC^2

    \Rightarrow FN = CP = \sqrt{\Big(\frac{6}{\tan a}\Big)^2- 12^2}=\sqrt{\frac{36}{\tan^2a}-144}

    Grandad
    Attached Thumbnails Attached Thumbnails 3D trig-untitled.jpg  
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