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Simple Vectors Triangle Rule Question!

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    It has been a few years since I have had to look at vectors, but I have got stuck on the first page of my textbook, and there is no working out in there to help me. Any help would be greatly appreciated.

    The magnitudes of the vectors shown are ¦U¦ = 8 and ¦V¦ = 3. The vector V is vertical. The vector U goes up at a 45 degree angle. Graphically determine the magnitude of the vector U-2V.

    Answer: 5.7

    Now the triangle rule states that I should use U-V. However that doesn't give the right answer.

    I tried using the sin and cosine rules to get there by doing sin(45)/6=sin(x)/8 and going from there but that does not give me the right answer either.

    Am I going wrong? please help! Thank you!
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    Just draw it like this and apply the cosine rule. You should get the right answer.

    Name:  VECTOR.PNG
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