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C4 Vectors Question

image.jpg
What does it mean by "between diagonals of the parallelogram"?
I did scalar product of AB and AC though I got the wrong answer. I tried other vectors though I kept getting an error whenever I subbed the values in my calculator.
You just need to find the angle between AB and AC, I think. It's the dot product divided by the product of the magnitudes of the vectors, if that makes sense
Reply 2
If you draw a line from one corner to the opposite corner of the parallelogram,that's a diagonal. Repeat for the other 2 corners and that's he othe diagonal. They meet at a point and you're finding the acute angle between them, not the obtuse angle.
Reply 3
What answer did you get?
Reply 4
Original post by L-Tyrosine
You just need to find the angle between AB and AC, I think. It's the dot product divided by the product of the magnitudes of the vectors, if that makes sense


Done that but not got the same answer as one in mark scheme


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Reply 5
Original post by B_9710
What answer did you get?


I got 35
The m.s. says 58.5


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Reply 6
Original post by TSRforum
image.jpg
What does it mean by "between diagonals of the parallelogram"?
I did scalar product of AB and AC though I got the wrong answer. I tried other vectors though I kept getting an error whenever I subbed the values in my calculator.


post your work please
Reply 7
Original post by TeeEm
post your work please


ImageUploadedByStudent Room1455232702.522685.jpg
Edit: should be root 29 instead of 53


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(edited 8 years ago)
Reply 8


I am sorry but I cannot make up from that what are you doing.
I expect to see the vectors for the diagonals first (or equivalent direction vectors)
Reply 9
Original post by TeeEm
I am sorry but I cannot make up from that what are you doing.
I expect to see the vectors for the diagonals first (or equivalent direction vectors)


ImageUploadedByStudent Room1455233105.166163.jpg
I just divided AC by 2 to get I + 2J +3/2K. I really don't know what acute angle I'm looking for ...




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(edited 8 years ago)
Reply 10
Original post by TSRforum
ImageUploadedByStudent Room1455233105.166163.jpg
I just divided AC by 2 to get I + 2J +3/2K. I really don't know what acute angle I'm looking for ...



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you need the vector BC or CB (the other diagonal)
Reply 11
Original post by TeeEm
you need the vector BC or CB (the other diagonal)


That's just -AC + AB, right? So it's -3i + -4j +0k. What do I do with that?


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Reply 12
Original post by TSRforum
That's just -AC + AB, right? So it's -3i + -4j +0k. What do I do with that?


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correct
dot it with AD
Reply 13
Original post by TeeEm
correct
dot it with AD


Got math error in calculator


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Reply 14
Original post by TSRforum
Got math error in calculator


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I cannot see what your are inputting
Do you know how to dot vectors?
Reply 15
Original post by TeeEm
I cannot see what your are inputting
Do you know how to dot vectors?


Yes. ImageUploadedByStudent Room1455234218.088783.jpg
ImageUploadedByStudent Room1455234253.185728.jpg
ImageUploadedByStudent Room1455234276.685708.jpg


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Reply 16


check the dot product
Reply 17
Original post by TeeEm
check the dot product


Oh I added instead of multiplying 😐


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