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Homework Help: Finding equation of both lines

  1. Mar 21, 2010 #1
    1. The problem statement, all variables and given/known data

    Determine the equation of both lines that are tangent to the graph of y=x^2 +4 and pass through the point (1,-2)

    2. Relevant equations

    3. The attempt at a solution

    The derivative/slope of the tangent is 2x. But I'm not too sure what to do with this.
  2. jcsd
  3. Mar 21, 2010 #2


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    Ok so let (x,y) be a point on your curve. That makes it (x,x^2+4), right? Now find the slope of the line between that point and (1,-2). That slope should be your 2x, also right? Now solve for x.
  4. Mar 22, 2010 #3
    Alright. Once I find x, what do I do with it?.

    Btw, the slope for that line is (x-1)/(x^2+6) rite?
  5. Mar 22, 2010 #4


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    Slope is delta(y)/delta(x), isn't it? Once you find values for x, each one gives you a point on the curve that also goes through (1,-2). Use the points to find the line equations.
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