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Math Help - Help with tangent line to a trig function

  1. #1
    Junior Member
    Joined
    Dec 2008
    Posts
    28

    Help with tangent line to a trig function

    The problem is: find the equation of a tangent line to the function y = cos2x
    at the point (pi/6, .5)

    i took the derivative and got -2sin2x plugged pi/6 in and got the slope to be
    -(3)^.5

    so i have the line y= x * -(3)^.5 + b and i plug in pi/6 for x and .5 for y and get

    .5 = -(3)^.5 * pi/6 + b

    so b = .5 + (3)^.5 * pi/6

    i put the line equation and the original trig equation in my calculator and the line is not tangent to cos2x at that point

    can someone please show me what i'm doing wrong, thank you
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  2. #2
    Junior Member
    Joined
    Dec 2008
    Posts
    28

    nvm i figured it out

    Ok wow nvm guys, i just put my line EQ in my calc and now its tangent >.< I'm sorry.
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