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Math Help - Angle between 2 lines proof

  1. #1
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    Angle between 2 lines proof

    Let L1 and L2 be two lines in the plane, with equations y = m1x + c1 and y = m2x + c2 respectively. Suppose that they intersect at an acute angle θ. Show that

    \tan\theta = |\frac{m_1-m_2}{1+m_1m_2}|

    Help please, I've drawn a diagram but I don't really know how to proceed.
    Thanks in advance
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  2. #2
    MHF Contributor Also sprach Zarathustra's Avatar
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    Re: Angle between 2 lines proof

    Quote Originally Posted by elieh View Post
    Let L1 and L2 be two lines in the plane, with equations y = m1x + c1 and y = m2x + c2 respectively. Suppose that they intersect at an acute angle θ. Show that

    \tan\theta = |\frac{m_1-m_2}{1+m_1m_2}|

    Help please, I've drawn a diagram but I don't really know how to proceed.
    Thanks in advance

    Here:

    Angle Between Two Lines
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  3. #3
    Member
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    Re: Angle between 2 lines proof

    if\alpha_1and\alpha_2 are inclinations of the lines use the fact that
    m_1=\tan\alpha_1&m_2=\tan\alpha_2
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