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Tangent problem

  1. Feb 24, 2005 #1
    Using the formula relating the tangent of angle p enclosed between two given straight line L1 and L2 and respective slope m1 and m2,Find the measure in degrees of angles A and C of the triangle with vertices A(-3,4),B(5,6) and C(2,1)

    My work is
    Tan A = Ma = yb-ya/xb-xa=6-4/5+3=2/8=1/4
    Tan A =1/4

    Tan C = Mb = yb-yc/xb-xc=5/3
    Tan C = 5/3

    So Angle A = arctan 1/4
    Angle C = arctan 5/3

    Any idea on this?
  2. jcsd
  3. Feb 25, 2005 #2


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    Science Advisor

    Those are the slopes of the lines and so give the angle each line makes with the horizontal.
    For example, you have calculated, correctly, that the line from B to C makes an angle with the horizontal of arctan(5/3) and that the line from A to C makes an angle with the horizontal of arctan (5/3). Now draw a picture. You should see that the horizontal line through C makes 3 angles. The center is the angle C in the triangle. The arctangents are the other two angles. Use the fact that the total angle is 180 degrees (or pi radians).
  4. Feb 28, 2005 #3
    yah I got u'r point
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