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# C4 vector question Watch

1. https://983c9f06eb1f75af6e83364e092b...20C4%20OCR.pdf

For question 2ii we have to find an angle for ABC. The markscheme says AB.BC. However, when I do normal vector questions, I do the vectors coming out of the angle, i.e BA.BC. Why is this one different or do I have the wrong approach?
Thank you
2. (Original post by snmk007)
https://983c9f06eb1f75af6e83364e092b...20C4%20OCR.pdf

For question 2ii we have to find an angle for ABC. The markscheme says AB.BC. However, when I do normal vector questions, I do the vectors coming out of the angle, i.e BA.BC. Why is this one different or do I have the wrong approach?
Thank you
Can you pass me the mark scheme?
3. (Original post by ChirMu)
Can you pass me the mark scheme?
https://983c9f06eb1f75af6e83364e092b...20C4%20OCR.pdf

Thanks
4. (Original post by snmk007)
https://983c9f06eb1f75af6e83364e092b...20C4%20OCR.pdf

For question 2ii we have to find an angle for ABC. The markscheme says AB.BC. However, when I do normal vector questions, I do the vectors coming out of the angle, i.e BA.BC. Why is this one different or do I have the wrong approach?
Thank you
I have checked the two methods and both are correct.
5. (Original post by ChirMu)
I have checked the two methods and both are correct.
Thanjks so much, I just did an error in my working
6. (Original post by snmk007)
Thanjks so much, I just did an error in my working
You're welcome
7. (Original post by snmk007)
https://983c9f06eb1f75af6e83364e092b...20C4%20OCR.pdf

For question 2ii we have to find an angle for ABC. The markscheme says AB.BC. However, when I do normal vector questions, I do the vectors coming out of the angle, i.e BA.BC. Why is this one different or do I have the wrong approach?
Thank you
The method you use is the correct one for ALL cases. However, when the angle between 2 lines is 90 or 180 degrees, then options to use the head-to-tail vector approach becomes correct as well. I've attached an image to to show you what I mean.

8. (Original post by RDKGames)
The method you use is the correct one for ALL cases. However, when the angle between 2 lines is 90 or 180 degrees, then options to use the head-to-tail vector approach becomes correct as well. I've attached an image to to show you what I mean.

Thanks soo much

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