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Problem with equation of line tangent to curve

  1. Sep 18, 2013 #1
    1. The problem statement, all variables and given/known data
    Now use your answer from part (a)(This anwser is f'(25) = 7/10, which is correct) to find the equation of the tangent line to the curve at the point (25, f(25)).


    2. Relevant equations
    f(x) = 7*sqrt(x)+3



    3. The attempt at a solution
    f'(25) = 7/10
    f(25) = 38
    y=mx+b
    38=7/10*25+b

    y=7/10x + 41/2

    This should be the correct answer... but it won't accept it.


    if you want to view the entire problem, http://i.imgur.com/xtVehti.png
     
  2. jcsd
  3. Sep 18, 2013 #2
    Try using something other than y=mx+b. Do you know any other ways to write the equation that doesn't rely on B?
     
  4. Sep 18, 2013 #3
    we are given y= ???

    so y=mx+b is really the only linear function they could be looking for.
     
  5. Sep 18, 2013 #4
    Try y-y_1=m(x-x_1). You are given y_1 and x_1 (or can easily find them) and you have already solved for m. The rest is plugging in and simplifying.
     
  6. Sep 18, 2013 #5
    edit: i am an idiot... had a - instead of a +
     
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