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    (Original post by Deeboss)
    QUESTION 19)

    Ok so this is the following method I have used.


    2D vector v rotated by 2x2 rotation matrix R will be the 2D vector v' as follows:
    v' = R v
    2x2 rotation matrix R is as follows, where is the rotation angle.


    My answer was.

    R = 3.76 -11.28 (2.dp)
    19.73 7.52

    Sorry about my terrible 2x2 matrix above, I dont know how to use the actual symbols on student room. Please check my answer and let me know!

    R12 = -11.28?
    Your answer doesn't seem to have anything to do with the question. The elements of the matrix, including r12, will all be values between -1 and 1 inclusive.
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    (Original post by ghostwalker)
    Your answer doesn't seem to have anything to do with the question. The elements of the matrix, including r12, will all be values between -1 and 1 inclusive.
    How do you work out they will all be values between -1 and 1? What is your method?
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    (Original post by Deeboss)
    How do you work out they will all be values between -1 and 1? What is your method?
    A rotation matrix consists of sines and cosines, hence their value must be between -1 and 1. You actually have it in your first post!
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    (Original post by ghostwalker)
    A rotation matrix consists of sines and cosines, hence their value must be between -1 and 1. You actually have it in your first post!
    I dont understand then? How is my answer wrong? -sin (70 degrees) x 12 = -11.28 (2.dp) Wouldnt this be the value for element r12 to 2.dp?

    Again sorry I dont mean to sound like I am right or wrong just trying to get my head around this
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    (Original post by Deeboss)
    I dont understand then? How is my answer wrong? -sin (70 degrees) x 12 = -11.28 (2.dp) Wouldnt this be the value for element r12 to 2.dp?

    Again sorry I dont mean to sound like I am right or wrong just trying to get my head around this
    Why are you multiplying it by 12?

    r_{12} is the name of the element in row 1, column 2.
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    (Original post by ghostwalker)
    Why are you multiplying it by 12?

    r_{12} is the name of the element in row 1, column 2.
    Well if there is no value to the r12 element how do I work that out? What do I multiply -sin70 by?
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    (Original post by Deeboss)
    Well if there is no value to the r12 element how do I work that out? What do I multiply -sin70 by?
    You don't need to multiply it by anything.

    r_{12}= -\sin\theta

    The question is asking you to find the value of the element in row1 column2 of the matrix. They call that element r_{12}

    It's standard terminology for the elements of a matrix to have two subscripts; the first refers to the row and the second to the column.
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    (Original post by ghostwalker)
    You don't need to multiply it by anything.

    r_{12}= -\sin\theta

    The question is asking you to find the value of the element in row1 column2 of the matrix. They call that element r_{12}

    It's standard terminology for the elements of a matrix to have two subscripts; the first refers to the row and the second to the column.
    Ohhh okaay. So it would only just be -sin 70? Which gives me an answer to -0.94 (2.dp)
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    (Original post by Deeboss)
    Ohhh okaay. So it would only just be -sin 70? Which gives me an answer to -0.94 (2.dp)
    is that correct ghostwalker? My most previous post?
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    (Original post by Deeboss)
    is that correct ghostwalker? My most previous post?
    Yep.
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    (Original post by ghostwalker)
    Yep.
    Dude, regardless of the work. I just wanted to say thanks for helping me out with this. Have a great week bro.
 
 
 
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