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    help pleaseAttachment 617592
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    RDKGames
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    (Original post by mervin101)
    help pleaseAttachment 617592
    Thread moved to maths. Please post in the maths forum for maths subject questions, thanks

    For this question, can you tell us what you've tried and post your working?
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    (Original post by mervin101)
    help please
    The difference between u_2 and u_1 is the same as the difference between u_3 and u_2
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    (Original post by RDKGames)
    The difference between u_2 and u_1 is the same as the difference between u_3 and u_2
    is that something i have to remember?
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    (Original post by mervin101)
    is that something i have to remember?
    Of course. That's a fundamental property of an arithmetic sequence - the difference between each term is the same.
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    (Original post by RDKGames)
    Of course. That's a fundamental property of an arithmetic sequence - the difference between each term is the same.

    so i wrote out this:
    u3-u2 = u2-u1

    so

    (4k+1) - (2k+5) = (2k+5) - (k-2)

    obviously i have to show k=11 so do I group the k terms and numbers?
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    (Original post by mervin101)
    so i wrote out this:
    u3-u2 = u2-u1

    so

    (4k+1) - (2k+5) = (2k+5) - (k-2)

    obviously i have to show k=11 so do I group the k terms and numbers?
    Yes, just solve for k.
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    (Original post by RDKGames)
    Yes, just solve for k.
    i have done A but how do i do b? is it differentiation? does f''(x) mean differentiate second principle

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    (Original post by mervin101)
    i have done A but how do i do b? is it differentiation? does f''(x) mean differentiate second principle
    f''(x) denotes the second derivative of f(x) - which can be equivalently called to be the first derivative of f'(x). So yes just differentiate again.
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    (Original post by RDKGames)
    f''(x) denotes the second derivative of f(x) - which can be equivalently called to be the first derivative of f'(x). So yes just differentiate again.
    thanks
    i got f''(x) = 8+2x^-3

    so that ^ was the second differential but what was the first? was it the function given? or 8x - x^-2 ?
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    (Original post by mervin101)
    thanks
    i got f''(x) = 8+2x^-3

    so that ^ was the second differential but what was the first? was it the function given? or 8x - x^-2 ?
    The first derivative is given by f'(x) as I told you so yes it is 8x-x^{-2}, but if you meant what the original function is, you need to integrate the first derivative function.
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    (Original post by RDKGames)
    The first derivative is given by f'(x) as I told you so yes it is 8x-x^{-2}, but if you meant what the original function is, you need to integrate the original function.

    i understand now thank you

    for c) to find f(x) do i integrate 8x-x^-2?

    its 7 marks and im clueless
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    (Original post by mervin101)
    i understand now thank you

    for c) to find f(x) do i integrate 8x-x^-2?

    its 7 marks and im clueless
    Yes..
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    (Original post by RDKGames)
    Yes..
    but i dont understand the question
    at first i thought "determine an equation of the curve" meant use the equation of a line (y-y1=m(x-x1)
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    y-y1=m(x-x1) is for finding the equation of a line. The question wants you to find the formula of a curve.
    As y=f(x) you can the equation of the curve by integrating f'(x).
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    (Original post by TheFirstOrder)
    y-y1=m(x-x1) is for finding the equation of a line. The question wants you to find the formula of a curve.
    As y=f(x) you can the equation of the curve by integrating f'(x).
    Understood. So generally when I am asked to find the equation of a curve must I integrate?
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    (Original post by mervin101)
    Understood. So generally when I am asked to find the equation of a curve must I integrate?
    Depends on the context.
 
 
 
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