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Section 12.2 Assignment 2

  1. Describe these lines as offset spans. Everything is in \(\RR^3\text{.}\) (6)

    1. The line through \((0,3,2)\) with direction \((-4,-4,1)\text{.}\)

    2. The line perpendicular to the plane \(5x - y + 3z = 0\) and through the point \((-2,2,-7)\text{.}\)

    3. The line which is the intersection of th planes \(-4x + 5y - z = 0\) and \(3x - y + z = 0\text{.}\)

  2. Find equations for these planes. (9)

    1. The plane parallel to \(x - y - z = 0\) but three units away in the positive \(z\) direction.

    2. The plane with normal \((-1,-5,3)\) through the point \((2,2,2)\text{.}\)

    3. The plane through the points \((-1,1,0)\text{,}\) \((-2,-2,1)\) and \((3,4,-4)\)

  3. Two planes \(P_1\) and \(P_2\) have normals \(n_1\) and \(n_2\text{.}\) What can you say about \(n_1 \times n_2\text{?}\) (4)

  4. Prove the following statments for vectors in \(\RR^3\text{.}\) (18)

    1. \begin{equation*} u \times (v + w) = (u \times v) + (u \times w) \end{equation*}

    2. \begin{equation*} u \times (v \times w) = (u \cdot w) v - (u \cdot v) w \end{equation*}

    3. \begin{equation*} u \times (v \times w) + v \times (w \times u) + w \times (u \times v) = 0 \end{equation*}

  5. How does the matrix

    \begin{equation*} M = \begin{pmatrix} 0 \amp 3 \amp -1 \\ -2 \amp 1 \amp 1 \\ -1 \amp 0 \amp 3 \end{pmatrix} \end{equation*}

    act on the following vectors.

    \begin{align*} a) \amp v = \begin{pmatrix} 0 \\ 0 \\ -5 \end{pmatrix} \amp b) \amp v = \begin{pmatrix} -1 \\ -1 \\ -1 \end{pmatrix} \amp c) \amp v = \begin{pmatrix} 7 \\ -12 \\ 4 \end{pmatrix} \amp d) \amp v = \begin{pmatrix} \dfrac{1}{5} \\ \dfrac{-3}{24} \\ \dfrac{-4}{5} \end{pmatrix} \end{align*}
  6. Use a computer to calculate the determinants of these matrices. Give me an interpretation of the resulting numbers. (If you do the matrices by hand, I'll give a couple of bonus marks). (6)

    \begin{align*} a) \amp \begin{vmatrix} 0 \amp -4 \amp 1 \\ 3 \amp -2 \amp -8 \\ 0 \amp 1 \amp 6 \end{vmatrix} \amp b) \amp \begin{vmatrix} 0 \amp 0 \amp 0 \amp 4 \\ -1 \amp -8 \amp 2 \amp 1 \\ 0 \amp 2 \amp 3 \amp 0 \\ -1 \amp -3 \amp -2 \amp 5 \end{vmatrix} \amp c) \amp \begin{vmatrix} \dfrac{1}{5} \amp \dfrac{2}{7} \amp 0 \\ \dfrac{-2}{3} \amp \dfrac{-2}{5} \amp \dfrac{1}{3} \\ \dfrac{-3}{4} \amp \dfrac{1}{4} \amp 0 \end{vmatrix} \end{align*}