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# as differentiation question watch

1. 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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2. (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?
3. Sorry my phone didn't post the picture the first time..

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4. (Original post by shiningsunset)
Sorry my phone didn't post the picture the first time..

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In part b .
5. (Original post by shiningsunset)
Sorry my phone didn't post the picture the first time..

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On (b) factorise the top see what you get, then compare the top and bottom brackets.
6. So you get y= x-3 but do you then have to differentiate this?

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7. (Original post by shiningsunset)
Sorry my phone didn't post the picture the first time..

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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.
8. (Original post by shiningsunset)
So you get y= x-3 but do you then have to differentiate this?

Posted from TSR Mobile
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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