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How to calculate angle in analytic geometry

  1. Jun 16, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img196.imageshack.us/img196/5391/29069034.jpg [Broken]

    2. Relevant equations

    only analytical methods

    3. The attempt at a solution
    I found k to be =2
    I don't have any idea how to calculate angle A.
    Please need some help.
    Thank You.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 16, 2009 #2
    You have several ways to solve this task, depends from your knowledge.
    y=kx+n is equation of line.

    you need to find k1 and k2 of the lines AC and AB.

    [tex]k=\frac{y_2-y_1}{x_2-x_1}[/tex]

    Also,
    [tex]tanA=\frac{k_2-k_1}{1+k1*k2}[/tex]

    Regards.
     
  4. Jun 16, 2009 #3
    Thanks I have found C[tex]\widehat{A}[/tex]B to be 52.1 and reflex [tex]\widehat{A}[/tex]
    307,9
     
  5. Jun 16, 2009 #4
    What is this equation called?
    [tex]tanA=\frac{k_2-k_1}{1+k1*k2}[/tex]

    Does this equation not resemble the compound angle identity of tan(A-B)?
     
  6. Jun 16, 2009 #5
    Its called formula for finding angle between two lines. Here is http://www.tpub.com/math2/5.htm" Yes, the formula is tan(A-B).

    [tex]k_2=tanA_2[/tex]

    [tex]k_1=tanA_1[/tex]
     
    Last edited by a moderator: Apr 24, 2017
  7. Jun 16, 2009 #6
    thanks again
     
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