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Math Help - Quick question about slope and finding f(x)

  1. #1
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    Quick question about slope and finding f(x)

    f(x) := ax˛ + bx + c
    find a, b, c ∈ R so that:
    for x=-1 f(x)=0, the slope at this point is 2
    and for x=1 f'(x)=0

    what i haven't encountered before is the expression, THE SLOPE AT THIS POINT IS 2. Does that mean that i take the derivative of the first equation f(x) and that for x=-1 f'(-1)=2, so -2a+b=2 ??

    the other two points are clear to me, a-b+c=0 and 2a+b=0
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    Re: Quick question about slope and finding f(x)

    It has been very clearly mentioned that slope at x=-1 is 2, so you have f'(-1)=2.

    That means b-2a=2.

    Solve the following equations to get the value of a,b and c.

    \begin{cases} a-b+c=0 \\ b-2a=2 \\ 2a+b=0 \end{cases}
    Last edited by sbhatnagar; December 11th 2011 at 02:42 AM.
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    Re: Quick question about slope and finding f(x)

    I know that but my qeustion was (maybe i didn't make it very clear..) when we know the VALUE of the SLOPE in a certain point X, does it translate to>> derivative f'(x) = value of slope, at that point?? Do i take the derivative to figure this out?
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    Re: Quick question about slope and finding f(x)

    Quote Originally Posted by nappysnake View Post
    I know that but my qeustion was (maybe i didn't make it very clear..) when we know the VALUE of the SLOPE in a certain point X, does it translate to>> derivative f'(x) = value of slope, at that point?? Do i take the derivative to figure this out?
    yes

    you'd need the derivative expression to utilize the slope information
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