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    I multiplied out the top to give x^2 - 5x - 24 over x.

    Now I'm confused because I differentiated it to give :
    2x-5 over 1 , but the answer involves subtracting the top from bottom :confused: . Why does subtracting happen before the differentiation ?
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    You can cancel this down further to x - 5 - 24/x, which is a much easier way to differentiate.

    This seems to be an AS question, it's not as simple when you have a quotient just to differentiate top and then bottom (explained at A2).
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    (Original post by WildBerry)


    ------

    I multiplied out the top to give x^2 - 5x - 24 over x.

    Now I'm confused because I differentiated it to give :
    2x-5 over 1 , but the answer involves subtracting the top from bottom :confused: . Why does subtracting happen before the differentiation ?
    Is this an AS question?
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    Yeah C1 question AS
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    (Original post by WildBerry)


    ------

    I multiplied out the top to give x^2 - 5x - 24 over x.

    Now I'm confused because I differentiated it to give :
    2x-5 over 1 , but the answer involves subtracting the top from bottom :confused: . Why does subtracting happen before the differentiation ?
     y = \frac{(x+3)(x-8)}{x}= \frac{x^2-5x-24}{x}= \frac{x^2}{x}- \frac{5x}{x} - \frac{24}{x} = x - 5 - \frac {24}{x}

    then

     \frac{dy}{dx} = 1 + \frac{24}{x^2}

    now do you understand?
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    (Original post by ilyking)
     y = \frac{(x+3)(x-8)}{x}= \frac{x^2-5x-24}{x}= \frac{x^2}{x}- \frac{5x}{x} - \frac{24}{x} = x - 5 - \frac {24}{x}

    then

     \frac{dy}{dx} = 1 + \frac{24}{x^2}

    now do you understand?
    Thanks alot , that made it seem much easier =)

    Yeah , y= is when its all subtracted out , dy/dx is that differntiated
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    (Original post by WildBerry)
    Thanks alot , that made it seem much easier =)

    Yeah , y= is when its all subtracted out , dy/dx is that differntiated
    subtracted isn't the right word. "Simplified" is.

    Just make sure you know when you start the differentiation process (simplify first completely, then begin the differentiated).

    Glad to help you :five:
 
 
 
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