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# is (b - a) and (a - b) the same in vectors ??

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1. So in my book they wrote
b- a
but I wrote a- b and I was wondering if they are both considered to be the same?

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2. They're the same in magnitude, but opposite in direction.
So in my book they wrote
b- a
but I wrote a- b and I was wondering if they are both considered to be the same?

No they are not the same because you wrote b as minus which it isn't as you travel in the direction the arrow is pointing in which means it is positive. Therefpre it can only be written as b-a or -a+b. Hope this helps!
4. (Original post by Speedbird129)
No they are not the same because you wrote b as minus which it isn't as you travel in the direction the arrow is pointing in which means it is positive. Therefpre it can only be written as b-a or -a+b. Hope this helps!
Okay then, so why is the answer b - a not a - b?
Okay then, so why is the answer b - a not a - b?
It is not a-b because to get from the start of the red dashed line to the end you have to travel along b in the direction the arrow is pointing, therefore b is positive. Then you travel down b in the opposite direction to the arrow, therefore it is negative. This is why b is positive and a is negative and therefore it is incorrect the other way round. Hope this helps!
6. (Original post by Speedbird129)
It is not a-b because to get from the start of the red dashed line to the end you have to travel along b in the direction the arrow is pointing, therefore b is positive. Then you travel down b in the opposite direction to the arrow, therefore it is negative. This is why b is positive and a is negative and therefore it is incorrect the other way round. Hope this helps!
Sorry, my mistake you travel down b and then a in the opposite direction to the arrow, therefore a is negative.
7. (Original post by Speedbird129)
Sorry, my mistake you travel down b and then a in the opposite direction to the arrow, therefore a is negative.
I still don't get it?
I still don't get it?
Is this for A-level?
I still don't get it?
b-a, on the diagram, is essentially moving from right to left (moving by vector b, then in the opposite direction of vector a). a-b ( a-b = -(b-a): moving by vector a, then moving in the opposite direction of vector b) is the vector moving from left to right.
10. Basically if you move in the direction that the arrow is pointing in, the letter has to be positive, therefore as you are moving through b in the direction that the arrow is pointing, b must be positive, not negative.
11. (Original post by Middriver)
Same size different directions Attachment 539983
Oh I see now!! Thank you!!
12. (Original post by Speedbird129)
Basically if you move in the direction that the arrow is pointing in, the letter has to be positive, therefore as you are moving through b in the direction that the arrow is pointing, b must be positive, not negative.
(Original post by oniisanitstoobig)
b-a, on the diagram, is essentially moving from right to left (moving by vector b, then in the opposite direction of vector a). a-b ( a-b = -(b-a): moving by vector a, then moving in the opposite direction of vector b) is the vector moving from left to right.
Thank you!!!
Oh I see now!! Thank you!!
No worries.
14. Thanks for the reps. Hope you understand now and is this for A-level?
15. (Original post by Speedbird129)
Thanks for the reps. Hope you understand now and is this for A-level?
Yep!! C4 vectors
Yep!! C4 vectors
Ok, I probably wasn't the best person to help as I am doing my GCSE's now but I would believe the basic principles are the same. Good luck in your studies and exams!

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