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# Curved surface FP2 watch

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1. http://filestore.aqa.org.uk/subjects...W-QP-JUN11.PDF

Question 5.

I'm sitting on S = 2πy∫√(1 +x^2/(x^2+8))

And i'm struggling to get to what they want me to show.

Help pls
2. (Original post by Bobjim12)
http://filestore.aqa.org.uk/subjects...W-QP-JUN11.PDF

Question 5.

I'm sitting on S = 2πy∫√(1 +x^2/(x^2+8))

And i'm struggling to get to what they want me to show.

Help pls
I'm very alarmed by the fact that you have the outside the integral sign... correct version:

3. (Original post by Zacken)
I'm very alarmed by the fact that you have the outside the integral sign... correct version:

i can never tell when we can just ignore the minus root, in this case y has two values............ this makes me sad.
4. (Original post by Bobjim12)
i can never tell when we can just ignore the minus root, in this case y has two values............ this makes me sad.
It would have made no difference had you taken the negative root - you'd get a negative area from which (I hope) you'd take the absolute value of to get the positive answer anyway. But at A-Level, you're nearly always going to be taking the positive root without any justification.

In either case - y is inside the integral!
5. (Original post by Zacken)
It would have made no difference had you taken the negative root - you'd get a negative area from which (I hope) you'd take the absolute value of to get the positive answer anyway. But at A-Level, you're nearly always going to be taking the positive root without any justification.

In either case - y is inside the integral!

ok ty

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