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Homework Help: Equation of tagent line when x is given, but not Y.

  1. Feb 23, 2009 #1
    1. The problem statement, all variables and given/known data
    Find the equation of the line tangent to y=(x²+3x)² (2x-2)³, when x=8


    2. Relevant equations



    3. The attempt at a solution
    dy/dx = 56x^6+144x^5-240x^4-320x^3+504x^2-144x......or........8x(x+3)(x+2)(7x-3)(x-1)²
    dy/dx (8) = 18282880
    y(x) = 21249536

    Equation of tangent line at x=8;
    y= 18282880x - 125013504

    The problem is that this is a calc 1 question, 2 months in. There seems to be an odd space between the (x²+3x)² and (2x-2)³. I think the teacher might forgot to put a + or a - in the problem. What do you all think?

    If I use a minus, I get a perfect 5000 for y(8). Making the end equation
    y=2168x-12344.

    Am I doing something wrong?
     
    Last edited: Feb 23, 2009
  2. jcsd
  3. Feb 23, 2009 #2

    Gib Z

    User Avatar
    Homework Helper

    If thats how the question was given, thats how it should be answered. Its not your job to try guess their typos =]
     
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