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Find which value of x horizontal Tangent Line

  1. Apr 28, 2010 #1
    Find which value of x....horizontal Tangent Line

    1. The problem statement, all variables and given/known data
    What is given is F(x)= -4/(x-3)(x+4) and the problem asks for to find the value of x where f(x) has a horizontal tangent line.


    2. Relevant equations
    I read somewhere else on these forms that using the quotient rule is the key, and that you make F'(x) to be equal to 0. If this is correct, I need some clarification on how it'd be put into the formula.
     
  2. jcsd
  3. Apr 28, 2010 #2

    rock.freak667

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    Re: Find which value of x....horizontal Tangent Line

    Well yes a horizontal tangent line, means that the gradient of the tangent at that point is zero, so F'(x)=0.

    But you don't necessarily need to use the quotient rule, the chain rule would suffice as well.


    So first find, F'(x)
     
  4. Apr 28, 2010 #3
    Re: Find which value of x....horizontal Tangent Line

    So, that means the left side is euqal to zero, or is every where (including left side) that is f '(x) is equal to zero. Or, am I looking for the derivative, but anywhere in the formula I see that has f ' (x) is simply zero. Thanks in advance.
     
  5. Apr 28, 2010 #4

    rock.freak667

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    Re: Find which value of x....horizontal Tangent Line

    Just find the expression for F'(x) and just equate that expression to zero and solve for x.
     
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