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    I'v done a, just need help with b. I think that I may have rearranged wrong before differentiating it, so could somebody help?
    Thanks


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    (Original post by shiningsunset)
    I'v done a, just need help with b. I think that I may have rearranged wrong before differentiating it, so could somebody help?
    Thanks


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    Can you post the question?
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    (Original post by shiningsunset)
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    In part b  y=x-3 .
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    (Original post by shiningsunset)
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    On (b) factorise the top see what you get, then compare the top and bottom brackets.
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    So you get y= x-3 but do you then have to differentiate this?


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    (Original post by shiningsunset)
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    Notice that x^2-9 has a factor of (x+3), ie. (x+3)(x-3) ≡ x^2 - 9, which cancels to x-3 as the user above mentioned.
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    (Original post by shiningsunset)
    So you get y= x-3 but do you then have to differentiate this?


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    Yes, differentiate and substitute in the value given, ie. x=4. In this case, you should get a constant, so it won't change.
 
 
 
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