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Math Help - tan A

  1. #1
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    tan A

    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 A. Show that

    tan A = (m1-m2)/(1+m1m2) <-- modulus of this

    The lines and modulus shows that I should use the formula for cos A with the dot product etc. But I am not sure what the dot product will be.

    Any hints?
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  2. #2
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    Hello Aquafina
    Quote Originally Posted by Aquafina 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 A. Show that

    tan A = (m1-m2)/(1+m1m2) <-- modulus of this

    The lines and modulus shows that I should use the formula for cos A with the dot product etc. But I am not sure what the dot product will be.

    Any hints?
    This is a very similar question to this one. Use the same method as I have done there, and the result follows immediately. (Don't try to use dot product!)

    Grandad
    Last edited by Grandad; October 31st 2009 at 02:40 AM. Reason: Fix typo
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