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c4 vectors



In part a) (not show in the above image), they ask you to find the lengths of AB and BC. I done that correctly.. For part b, when constructing the above diagram, how do you know which way the arrows point?

Thanks
Reply 1
Avatar for raheem94
raheem94
13
Original post by xXxiKillxXx


In part a) (not show in the above image), they ask you to find the lengths of AB and BC. I done that correctly.. For part b, when constructing the above diagram, how do you know which way the arrows point?

Thanks


The arrows should be pointing away from B, hence the arrows are in the direction BA and BC.
Reply 2
Avatar for xXxiKillxXx
xXxiKillxXx
OP
14
Original post by raheem94
The arrows should be pointing away from B, hence the arrows are in the direction BA and BC.


Why should they be pointing away from B? THanks
Reply 3
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raheem94
13
Original post by xXxiKillxXx
Why should they be pointing away from B? THanks


See page#69 of the edexcel C4 book.
Reply 4
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xXxiKillxXx
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14
Original post by raheem94
See page#69 of the edexcel C4 book.


Oh so vectors always point away from the angle?
Reply 5
Avatar for raheem94
raheem94
13
Original post by xXxiKillxXx
Oh so vectors always point away from the angle?


If you want to find angle ABC.

Then the two vectors you need to consider should be in the direction pointing away from B.

AB is pointing towards B, so we use BA rather than AB.
CB is pointing towards B, so we use BC rather than CB.
Reply 6
Avatar for user977153
user977153
Work out BA and BC and use the costheta formula.
Reply 7
Avatar for xXxiKillxXx
xXxiKillxXx
OP
14
Original post by raheem94
If you want to find angle ABC.

Then the two vectors you need to consider should be in the direction pointing away from B.

AB is pointing towards B, so we use BA rather than AB.
CB is pointing towards B, so we use BC rather than CB.



Original post by DoctorVertigo
Work out BA and BC and use the costheta formula.


Ahhh thanks :smile:

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