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Math Help - Vector Magnitude and Angle at 0x

  1. #1
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    Vector Magnitude and Angle at 0x

    Sorry if this isn't pre-calc, the education system over here is different =\ .

    Just checking if I have this right as our instructions and teachings were a bit vague.

    Question: Given that a = i + j and b = 2i + j, find the magnitude of each of the following vectors and the angle each makes with Ox.

    (d) : 3a - 2b

    My answer:
    Magnitude : sqrt(26)
    Angle: 101.3 degrees (3sf)
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  2. #2
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    Quote Originally Posted by Viral View Post
    Question: Given that a = i + j and b = 2i + j, find the magnitude of each of the following vectors and the angle each makes with Ox.
    (d) : 3a - 2b
    You need to rework the problem because 3a-2b=-i+j.
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  3. #3
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    Quote Originally Posted by Plato View Post
    You need to rework the problem because 3a-2b=-i+j.
    What do you mean rework?

    From what I can see, the lengh on the x axis would be 1, while the height on the y-axis would be 1 as well. However, as it is -1i, it would be on the negative x axis. So does this make a difference to the normal way of working it out?

    I did:

    3(i+j) - 2(2i-j)
    = (3i+3j) - (4i - 2j)
    = |-i + 5j|
    = sqrt(i^2 + 5^2)
    = sqrt(26)
    angle = 180 - tan^-1(5)
    angle = 101.3 degrees

    The problem is, I'm not sure if I was supposed to do the 180- part or not?
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  4. #4
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    Quote Originally Posted by Viral View Post
    What do you mean rework?

    From what I can see, the lengh on the x axis would be 1, while the height on the y-axis would be 1 as well. However, as it is -1i, it would be on the negative x axis. So does this make a difference to the normal way of working it out?

    I did:

    3(i+j) - 2(2i-j)
    = (3i+3j) - (4i - 2j)
    = |-i + 5j|
    = sqrt(i^2 + 5^2)
    = sqrt(26)
    angle = 180 - tan^-1(5)
    angle = 101.3 degrees

    The problem is, I'm not sure if I was supposed to do the 180- part or not?
    The problem says that \color{blue}b=2i\large+j
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  5. #5
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    Hmm that was a typo in the first post.

    a = i + j
    b = 2i - j
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