# FP3: ellipseWatch

#1
so,

I'm at the point attached, but that looks nothing like the answer.

that's meant to be -3sin(theta)
Last edited by Maths&physics; 1 week ago
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1 week ago
#2
Post your working. (And if you can't use LaTeX, take a photo of your writing and post that. The near illegible scrawls you've been posting are insufficient).
1
#3
(Original post by DFranklin)
Post your working. (And if you can't use LaTeX, take a photo of your writing and post that. The near illegible scrawls you've been posting are insufficient).
can you see this?
0
1 week ago
#4
You've used the formula for the volume of revolution, not the surface area.

I find myself repeatedly having to ask this, but have you actually read the material for the topic you're trying to answer questions on?
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#5
(Original post by DFranklin)
You've used the formula for the volume of revolution, not the surface area.

I find myself repeatedly having to ask this, but have you actually read the material for the topic you're trying to answer questions on?
I have but it's been a while. I will go back and watch the tutorials again. thank you for help and please, I'm open to constructive criticism if it will help me.
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1 week ago
#6
(Original post by Maths&physics)
I have but it's been a while. I will go back and watch the tutorials again. thank you for help and please, I'm open to constructive criticism if it will help me.
The thing is, you can't sensibly attempt answer questions if you don't understand the material. You're answering a FP3 problem, and the formulas you need to use are described in the FP3 syllabus. Instead you've used a C4 formula that totally doesn't apply to the question. It's hard to say anything constructive when I honestly think this mistake is impossible to make if you've spent more than 5 minutes looking at the topic in the FP3 syllabus. (That is, I can see someone doing FP3 might struggle to know which FP3 formula to use, or how to evaluate the resulting integral etc., but the whole topic is about "extensions beyond the C4 formula", so I feel it's hard to know the first thing about the topic and make the mistake of using a C4 formula).

So my constructive advice would be to revise the topics before you try to answer questions on them.
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#7
(Original post by DFranklin)

So my constructive advice would be to revise the topics before you try to answer questions on them.
That's what I will be doing. thank you. I have looked at the topic and I now have the formulas.
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#8
(Original post by DFranklin)
The thing is, you can't sensibly attempt answer questions if you don't understand the material. You're answering a FP3 problem, and the formulas you need to use are described in the FP3 syllabus. Instead you've used a C4 formula that totally doesn't apply to the question. It's hard to say anything constructive when I honestly think this mistake is impossible to make if you've spent more than 5 minutes looking at the topic in the FP3 syllabus. (That is, I can see someone doing FP3 might struggle to know which FP3 formula to use, or how to evaluate the resulting integral etc., but the whole topic is about "extensions beyond the C4 formula", so I feel it's hard to know the first thing about the topic and make the mistake of using a C4 formula).

So my constructive advice would be to revise the topics before you try to answer questions on them.
so, for the equation of the surface area, we sub y into the equation. but in M3, with the solid of revolution, we multiple the equation by y (or x). why does this difference exist?
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1 week ago
#9
(Original post by Maths&physics)
so, for the equation of the surface area, we sub y into the equation. but in M3, with the solid of revolution, we multiple the equation by y (or x). why does this difference exist?
In M3 you are finding the CENTRE OF MASS, are you not??

Here you are finding only the volume/surface of recolution... which is obviously different from the COM ! Hence the difference..

Bit surprised you asked this tbh. The obvious answer is that there is a difference because these formulae describe different things.
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#10
(Original post by RDKGames)
In M3 you are finding the CENTRE OF MASS, are you not??

Here you are finding only the volume/surface of recolution... which is obviously different from the COM ! Hence the difference..

Bit surprised you asked this tbh. The obvious answer is that there is a difference because these formulae describe different things.
what is the logic behind substituting the y value into this equation and multiplying the equation by y in the COM equation?
0
1 week ago
#11
When are you taking your exam? Sounds like You’re talking about the old further maths spec that ended last year, unless you are retaking it?
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#12
(Original post by Gent2324)
When are you taking your exam? Sounds like You’re talking about the old further maths spec that ended last year, unless you are retaking it?
this is the old spec.
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1 week ago
#13
(Original post by Maths&amp;physics)
this is the old spec.
are you retaking the exam then?
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#14
(Original post by Gent2324)
are you retaking the exam then?
pretty much, it's a long story.
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1 week ago
#15
(Original post by Maths&physics)
what is the logic behind substituting the y value into this equation and multiplying the equation by y in the COM equation?
Where the equations come from should be explained in the theory in your textbook.

Otherwise, seek those explanations online. Diagrams are useful for these explanation so it's best you try and find them off this site.
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#16
(Original post by RDKGames)
Where the equations come from should be explained in the theory in your textbook.

Otherwise, seek those explanations online. Diagrams are useful for these explanation so it's best you try and find them off this site.
ok, thanks.
Last edited by Maths&physics; 1 week ago
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