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# M1 Vectors question(Urgent) watch

1. An aeroplane flies from airport A to airport B 80 km away on a bearing of 070∘. From B the aeroplane flies to airport C, 60 km from B. Airport C is 90 km from A. Find the two possible directions for the course set by the aeroplane on the second stage of its journey.

Okay, here's the thing. I'm guessing all I need here is the bearing of airport C from airport A. The thing is when I try finding the bearing using cosine rule I keep getting a math error. Heres what I did. I used the cosine rule to find the angle BAC. I used the following values in the equation:
a=60km
b=80km
c=90km
A= unknown
When I plug in these values, I get a math error.
However, the solutionbank used the exact same method, but, what I really don't get is, why did they use these values?:
a=6, b=8, c=9
Using the above, they got the answer as 78.6
What happened there?
2. Lol, I'm getting 110.8 and 330.8 as bearings so beats me :/

Okay, you appear to have written the question down incorrectly, or the book has a mistake. The distance from a to b is 80, the distance from b to c is 90 and the distance from c to a is 60. With those values, you should get one of the bearings as 78.6. Make sure in the formula that you label the triangle correctly:
http://www.cimt.plymouth.ac.uk/proje...t4/nratbig.gif

The angle A must be opposite the line a.
3. I'm getting 78.6 as well even using the values that you said with 60, 80 and 90. It makes no difference with the ones from solutionbank because the ratio of numbers is still the same (? Someone correct me if I'm wrong here).

Is it possible that you mis-typed? Or you used the formula incorrectly?
4. (Original post by djpailo)
Lol, I'm getting 110.8 and 330.8 as bearings so beats me :/

Okay, you appear to have written the question down incorrectly, or the book has a mistake. The distance from a to b is 80, the distance from b to c is 90 and the distance from c to a is 60. With those values, you should get one of the bearings as 78.6. Make sure in the formula that you label the triangle correctly:
http://www.cimt.plymouth.ac.uk/proje...t4/nratbig.gif

The angle A must be opposite the line a.
Actually my book reads ".....From B the aeroplane flies to airport C, 60 km from B. Airport C is 90 km from A." So I am guessing as you said the book could be wrong
5. (Original post by h8skoooooool)
I'm getting 78.6 as well even using the values that you said with 60, 80 and 90. It makes no difference with the ones from solutionbank because the ratio of numbers is still the same (? Someone correct me if I'm wrong here).

Is it possible that you mis-typed? Or you used the formula incorrectly?
I'm guessing that could be it. Its something to do with the ratios. Thanks a lot for that

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