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# C4 Vectors and Scalar Products Tweet

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1. C4 Vectors and Scalar Products
Hi
I am really stuck on question 8 part C
I have tried using the formula for cos(theta) but i get the wrong answer
Any help will be much appreciated
Thankyou

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2. Re: C4 Vectors and Scalar Products
(Original post by Lanter)
Hi
I am really stuck on question 8 part C
I have tried using the formula for cos(theta) but i get the wrong answer
Any help will be much appreciated
Thankyou

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What were you using as your two vectors?
3. Re: C4 Vectors and Scalar Products
You might be using the wrong vectors
Find the vectors AB and AO then use the the dot product equation to find the angle.
Last edited by ReTurd; 29-05-2012 at 09:52.
4. Re: C4 Vectors and Scalar Products
Make sure both of the vectors have the same direction with regards to their intersection.
5. (Original post by Thrug)
What were you using as your two vectors?
Vectors a (2i+3j-1k) and b (-1i+6j+7k) that i worked out in the previous question
Sorry for the late reply btw

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6. (Original post by ReTurd)
You might be using the wrong vectors
Find the vectors AB and AO then use the the dot product equation to find the angle.
I will try that now

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7. (Original post by Classical Liberal)
Make sure both of the vectors have the same direction with regards to their intersection.
Ok thankyou

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8. Re: C4 Vectors and Scalar Products
(Original post by Lanter)
Ok thankyou

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You know you have them the wrong way round if you get an obtuse angle.

If you do just do [ 180 minus your answer ] to get back to acute.
9. (Original post by Thrug)
You know you have them the wrong way round if you get an obtuse angle.

If you do just do [ 180 minus your answer ] to get back to acute.
Yeah i know
Thanks anyways
Done the question now finally

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