# Can I use the dot product in A-Level Maths?Watch

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Thread starter 10 months ago
#1
I have a tedious 7 mark question to do with vectors, which can be solved in two lines using the dot product. Is this allowed? Or will I be penalised?
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10 months ago
#2
(Original post by blootle456)
I have a tedious 7 mark question to do with vectors, which can be solved in two lines using the dot product. Is this allowed? Or will I be penalised?
Don't see why not. Especially when the dot product is taught at A level.

EDIT: This is old info from back in my day
Last edited by NotNotBatman; 10 months ago
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10 months ago
#3
Dot product, inner product, or scalar product, is part of FM topic on vectors. Do you think FM students will be using this method if appropriate, on a Maths A-Level paper?
Strictly, you really shouldn't need to use dot product on a Current maths A-Level qn, but if you DO use it, of course there's no penalty. It's a valid method.
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10 months ago
#4
Unless the question specifically tells you NOT to use to Dot-Product, then you can use it.
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10 months ago
#5
(Original post by blootle456)
I have a tedious 7 mark question to do with vectors, which can be solved in two lines using the dot product. Is this allowed? Or will I be penalised?
It is allowed but can you please show us the question and tell us where you got it from?
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10 months ago
#6
(Original post by begbie68)
Dot product, inner product, or scalar product, is part of FM topic on vectors. Do you think FM students will be using this method if appropriate, on a Maths A-Level paper?
Strictly, you really shouldn't need to use dot product on a Current maths A-Level qn, but if you DO use it, of course there's no penalty. It's a valid method.
The dot product isn't in single maths anymore?
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10 months ago
#7
(Original post by NotNotBatman)
The dot product isn't in single maths anymore?
No most of C4 vectors has been moved to further maths.
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10 months ago
#8
(Original post by Notnek)
It is allowed but can you please show us the question and tell us where you got it from?
i assume the question is asking you to prove they are perpendicular
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10 months ago
#9
Here's one where there's no perpendicularity. 8 marks total. Very simple if we use "Further Maths" ....
(Original post by Gent2324)
i assume the question is asking you to prove they are perpendicular
Last edited by begbie68; 10 months ago
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10 months ago
#10
(Original post by begbie68)
Here's one where there's no perpendicularity. 8 marks total. Very simple if we use "Further Maths" ....
i literally just had that test last week, answer is not 93, its 127 or something.
the area is correct though, are u using the cross-product or something for that?i dont recognise it
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10 months ago
#11
thanks. i had been too lazy earlier to get my calc, so I used Windows Calc | 'scientific' ... won't be doing that again ....

cos(theta) is correct , just MS windows calc is bad at arcos .... anyway ... edited, now.

The area is from determinant of a matrix. Method can be proved easily using vectors. Cross product to do this in 3D just follows from this determinant result.
(Original post by Gent2324)
i literally just had that test last week, answer is not 93, its 127 or something.
the area is correct though, are u using the cross-product or something for that?i dont recognise it
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10 months ago
#12
(Original post by begbie68)
thanks. i had been too lazy earlier to get my calc, so I used Windows Calc | 'scientific' ... won't be doing that again ....

cos(theta) is correct , just MS windows calc is bad at arcos .... anyway ... edited, now.

The area is from determinant of a matrix. Method can be proved easily using vectors. Cross product to do this in 3D just follows from this determinant result.
Are you doing Edexcel fm? If so what topic is the determinent area matrix thing?

Just be aware that you can’t use the dot product for the last question because proving 2 lines are perpendicular doesn’t prove that they bisect each other.
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10 months ago
#13
I'm no longer a student....
but useful advice about that last question. Not sure if too many studes will be confused about the obvious differences between 'bisect' and 'perpendicular', but then I've known several to confuse the words/meanings of 'odd' and negative' when doing proofs....

I'd already done the question using GCSE vector method(s).

'Determinant area matrix thing' might not be an "exam-specific" part of the topic, but it's useful, anyway. I'm not sure if you'll find it in the text book.
(Original post by Gent2324)
Are you doing Edexcel fm? If so what topic is the determinent area matrix thing?

Just be aware that you can’t use the dot product for the last question because proving 2 lines are perpendicular doesn’t prove that they bisect each other.
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