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C4 vector question help !

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hi for part c I don't get why I will not get the A1 mark. I used da instead of AD. But why does this matter ? Why does the mark scheme does not allow this for the accuracy mark ? Thanks

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Reply 1

ghostwalker

Original post by coconut64

hi for part c I don't get why I will not get the A1 mark. I used da instead of AD. But why does this matter ? Why does the mark scheme does not allow this for the accuracy mark ? Thanks

Because, you could just as easily have used that working to show the angle is 71 degrees. Why did you subtract it from 180, other than to get the answer they wanted?

(edited 6 years ago)

Reply 2

Notnek

Original post by coconut64

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hi for part c I don't get why I will not get the A1 mark. I used da instead of AD. But why does this matter ? Why does the mark scheme does not allow this for the accuracy mark ? Thanks

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You may have already seen it but I wrote a guide to this question here. Look at my diagram for c) - the dot product formula gives you the angle between two vectors where they are pointing towards or away from each other so you need to dot AD with AB or DA with BA.

If you dot DA with AB then you'll end up with a different angle and you'd have to explain (maybe with the aid of a diagram) why you'd need to subtract from 180 to get the angle BAD.

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C4 vector question help !

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