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Math Help - solid of revolution and a matrix q

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    solid of revolution and a matrix q

    Hi guys, not sure if anyone can help me but i'm super stuck with two uestions for my up coming exam:

    Find the volume of the solid of revolution obtained by rotating, a full turn about the
    x-axis, the area between the x-axis and the curve y = 2 sin x, for x
    ∈ [π/4, 3π/4].

    and this one too

    Matrices A, B, C , D & X satisfy equation A(X + B)C = D, and D is a 55 matrix. If A has 3 columns, and C 4 rows, find the dimensions of each matrix. Give conditions on the matrices A, B, C & D, if necessary, to ensure that we can solve the above equation. Find an expression for the unknown matrix X .

    Thanks very much
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  2. #2
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    Quote Originally Posted by kate45 View Post
    Hi guys, not sure if anyone can help me but i'm super stuck with two uestions for my up coming exam:

    Find the volume of the solid of revolution obtained by rotating, a full turn about the
    x-axis, the area between the x-axis and the curve y = 2 sin x, for x
    ∈ [π/4, 3π/4].

    and this one too

    Matrices A, B, C , D & X satisfy equation A(X + B)C = D, and D is a 55 matrix. If A has 3 columns, and C 4 rows, find the dimensions of each matrix. Give conditions on the matrices A, B, C & D, if necessary, to ensure that we can solve the above equation. Find an expression for the unknown matrix X .

    Thanks very much

    For the first one use the disk method the function represents the radius of a circular disk with thickness dx. so we get

    V=\int_{\frac{\pi}{4}}^{\frac{3\pi}{4}}\pi(\sin(x)  )^2dx

    For part B

    we know that Matrix X and B must have the same dimention (why?)

    To multiply two matrices what conditions must be satisfied.

    Think about this and see what you can do.

    Good luck
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