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    If we hit a differentiation question in which the chain rule is easier, are we allowed to use it in the new AS maths Edexcel. Thanks
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    (Original post by brownguytorule)
    If we hit a differentiation question in which the chain rule is easier, are we allowed to use it in the new AS maths Edexcel. Thanks
    You shouldn't need to use it, but I don't think it would be a problem.

    Can you post an example of a question like that?
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    as long as your working is clear you can use any method ( unless they specifically tell you to use one method ).
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    (Original post by TheMindGarage)
    You shouldn't need to use it, but I don't think it would be a problem.

    Can you post an example of a question like that?
    y = 1/(x+1)
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    (Original post by brownguytorule)
    y = 1/(x+1)
    Fair enough - if I saw that, I'd use chain rule myself.
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    (Original post by brownguytorule)
    y = 1/(x+1)
    You wouldn't be asked to differentiate this in an AS maths exam. Did you come up with this or did you see this question somewhere?
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    (Original post by brownguytorule)
    y = 1/(x+1)
    What method were they expecting you to use? Assuming you saw this in an AS lesson.
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    (Original post by Notnek)
    You wouldn't be asked to differentiate this in an AS maths exam. Did you come up with this or did you see this question somewhere?
    our teacher randomly mentioned this in class but asked us how we would differentiate such an equation if we got it given.
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    (Original post by brownguytorule)
    our teacher randomly mentioned this in class but asked us how we would differentiate such an equation if we got it given.
    I'd imagine most students would just differentiate with respect to x+1, which would actually produce the right answer here because x+1 just differentiates to 1. A question will not demand the use of the chain rule, but I don't see any reason not to use it if you think it'll work out better. (which I again doubt) Probably just trying to get you thinking.
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    That is a good point _gcx.

    The only other way is to use first pricipals where the derivative is defined as:

     \displaystyle \lim_{h \rightarrow 0} \frac{ (f(x+h) - f(x)) } {h},

    if the limit exists.

    For our expression f(x) = 1 / (x+1):

     \displaystyle f^{'} (x) = \lim_{h \rightarrow 0} \frac{ \left( \frac{1}{(x+h)+1} - \frac{1}{x+1} \right) }{h},

     \displaystyle = \lim_{h \rightarrow 0} \frac{-1}{ ((x+h)+1)(x+1) },

     \displaystyle = \frac{-1}{(x+1)^{2}}.

    However, the AS-Level specification (for Edexcel, page 17) states: "Differentiation from first priciples for small positive integer powers of x".
 
 
 
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