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I can't really start reading up on this question as I don't know what topic it is. Can anyone help?

True or false: if u is perpendicular to v and w thenuis perpendicular tov+ 2w.Give a proof if true, or a counterexample if false

True or false: if u is perpendicular to v and w thenuis perpendicular tov+ 2w.Give a proof if true, or a counterexample if false

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#2

(Original post by

I can't really start reading up on this question as I don't know what topic it is. Can anyone help?

True or false: if u is perpendicular to v and w thenuis perpendicular tov+ 2w.Give a proof if true, or a counterexample if false

**IHopetoImprove**)I can't really start reading up on this question as I don't know what topic it is. Can anyone help?

True or false: if u is perpendicular to v and w thenuis perpendicular tov+ 2w.Give a proof if true, or a counterexample if false

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#3

**IHopetoImprove**)

I can't really start reading up on this question as I don't know what topic it is. Can anyone help?

True or false: if u is perpendicular to v and w thenuis perpendicular tov+ 2w.Give a proof if true, or a counterexample if false

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#5

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I mean I'm thinking vectors but that's a pretty big domain. And I'm not really sure what multiplying them would do? I don't really understand why u being perpendicular would mean you multipy. Nor can I visualise it being perpendicular to two things either, I really just need to know some background.

**IHopetoImprove**)I mean I'm thinking vectors but that's a pretty big domain. And I'm not really sure what multiplying them would do? I don't really understand why u being perpendicular would mean you multipy. Nor can I visualise it being perpendicular to two things either, I really just need to know some background.

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#7

(Original post by

Yes, or rather, what does this mean practically?

**IHopetoImprove**)Yes, or rather, what does this mean practically?

I would expect you know this if you are attempting this question?

With more theory, you would see that two vectors are perpendicular if their dot product is zero.

Last edited by RDKGames; 1 week ago

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#8

(Original post by

Yes, or rather, what does this mean practically?

**IHopetoImprove**)Yes, or rather, what does this mean practically?

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OK, that is more what I'm asking, their dot product is zero is useful info I can work from, thank you.

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OK, that is more what I'm asking, their dot product is zero is useful info I can work from, thank you.

Thank you.

(Original post by

I'd look for a counter-example. The dot product being zero has a caveat.

**ghostwalker**)I'd look for a counter-example. The dot product being zero has a caveat.

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#12

**IHopetoImprove**)

I mean I'm thinking vectors but that's a pretty big domain. And I'm not really sure what multiplying them would do? I don't really understand why u being perpendicular would mean you multipy. Nor can I visualise it being perpendicular to two things either, I really just need to know some background.

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#13

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Surely if you're being asked this question as part of a uni course then you've been given a context for it, i.e. you know what module you're studying and what objects you're working with?

**davros**)Surely if you're being asked this question as part of a uni course then you've been given a context for it, i.e. you know what module you're studying and what objects you're working with?

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#14

(Original post by

You know, I'm getting very concerned about the way Universities seem to be teaching mathematics these days. Apparently it's now the norm to set questions in areas that aren't covered in the course - indeed, speaking to the students it seems likely no mathematics at all has actually been covered since term started. What's more, there seem to be severe bandwidth limits on uploads, preventing the poor students from ever being able to upload anything even remotely resembling an attempt at answering a question.

**DFranklin**)You know, I'm getting very concerned about the way Universities seem to be teaching mathematics these days. Apparently it's now the norm to set questions in areas that aren't covered in the course - indeed, speaking to the students it seems likely no mathematics at all has actually been covered since term started. What's more, there seem to be severe bandwidth limits on uploads, preventing the poor students from ever being able to upload anything even remotely resembling an attempt at answering a question.

I have a lot of sympathy for new students not knowing how to structure a proof initially, or even knowing which parts of a complex definition can be lifted out to use in a proof, but if they aren't even given a clue as to their topic of investigation then things are really looking pretty bleak for them.

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**ghostwalker**)

I'd look for a counter-example. The dot product being zero has a caveat.

counter e.g. >> v = i + j , w = 2i + 2j

v * w = i * 2i + j * 2j = 2i + 2j ??? (not sure if this is correct at all)

v + 2w = (i + j) + (2i + 2j) = 3i + 3j != v*w

I don't see where perpendicularness comes into it?

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(Original post by

Surely if you're being asked this question as part of a uni course then you've been given a context for it, i.e. you know what module you're studying and what objects you're working with? I mean are you doing a Geometry course where vectors can be used to represent real physical entities like lines or sides of a shape and you can see what "perpendicular" means, or are you doing a more abstract linear algebra course where you're given a purely abstract definition of perpendicularity for two objects??

**davros**)Surely if you're being asked this question as part of a uni course then you've been given a context for it, i.e. you know what module you're studying and what objects you're working with? I mean are you doing a Geometry course where vectors can be used to represent real physical entities like lines or sides of a shape and you can see what "perpendicular" means, or are you doing a more abstract linear algebra course where you're given a purely abstract definition of perpendicularity for two objects??

I am 90% sure this is the wrong direction.

counter e.g. >> v = i + j , w = 2i + 2j

v * w = i * 2i + j * 2j = 2i + 2j ??? (not sure if this is correct at all)

v + 2w = (i + j) + (2i + 2j) = 3i + 3j != v*w

I don't see where perpendicularness comes into it?

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#17

(Original post by

I mean yes but I have probably with online teaching and everything missed where perpendicularness comes into things, I see you misunderstand me so let me show you what I mean.

I am 90% sure this is the wrong direction.

counter e.g. >> v = i + j , w = 2i + 2j

v * w = i * 2i + j * 2j = 2i + 2j ??? (not sure if this is correct at all)

v + 2w = (i + j) + (2i + 2j) = 3i + 3j != v*w

I don't see where perpendicularness comes into it?

**IHopetoImprove**)I mean yes but I have probably with online teaching and everything missed where perpendicularness comes into things, I see you misunderstand me so let me show you what I mean.

I am 90% sure this is the wrong direction.

counter e.g. >> v = i + j , w = 2i + 2j

v * w = i * 2i + j * 2j = 2i + 2j ??? (not sure if this is correct at all)

v + 2w = (i + j) + (2i + 2j) = 3i + 3j != v*w

I don't see where perpendicularness comes into it?

**you absolutely need a definition of what "perpendicular" means for your vectors**. And also you are supposed to be working with 3 vectors u, v and w, not just v and w, so what you've written above isn't a "proof" (or counterexample) for your original statement.

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#18

(Original post by

I mean yes but I have probably with online teaching and everything missed where perpendicularness comes into things, I see you misunderstand me so let me show you what I mean.

**IHopetoImprove**)I mean yes but I have probably with online teaching and everything missed where perpendicularness comes into things, I see you misunderstand me so let me show you what I mean.

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(Original post by

Well, as we suggested above,

**davros**)Well, as we suggested above,

**you absolutely need a definition of what "perpendicular" means for your vectors**. And also you are supposed to be working with 3 vectors u, v and w, not just v and w, so what you've written above isn't a "proof" (or counterexample) for your original statement.So my issue in the question is 2) that I have 0 bloody idea how perpendicularity plays into the problem hence I have no idea what u really does in the context of the question.

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(Original post by

Which subject are you studying and where? Did you do A-level Maths?

**DFranklin**)Which subject are you studying and where? Did you do A-level Maths?

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