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Find the values of lambda and mu for which the lines r = 3i - j + k + lambda(i + 2j - k) and r = 4i + 4j + k + mu(-i + j + 2k) intersect.

Mathematics

ScanSolve AI Answer

Answer

B

Step-by-step solution

4 steps

To find the values of λ\lambda and μ\mu for which the lines intersect, we set the position vectors equal to each other.

Given lines:
Line 1: r=3i−j+k+λ(i+2j−k)\mathbf{r} = 3\mathbf{i} - \mathbf{j} + \mathbf{k} + \lambda(\mathbf{i} + 2\mathbf{j} - \mathbf{k})
Line 2: r=4i+4j+k+μ(−i+j+2k)\mathbf{r} = 4\mathbf{i} + 4\mathbf{j} + \mathbf{k} + \mu(-\mathbf{i} + \mathbf{j} + 2\mathbf{k})

  1. Equate the position vectors.

    3i−j+k+λ(i+2j−k)=4i+4j+k+μ(−i+j+2k)3\mathbf{i} - \mathbf{j} + \mathbf{k} + \lambda(\mathbf{i} + 2\mathbf{j} - \mathbf{k}) = 4\mathbf{i} + 4\mathbf{j} + \mathbf{k} + \mu(-\mathbf{i} + \mathbf{j} + 2\mathbf{k})

    Expand and group terms by i\mathbf{i}, j\mathbf{j}, and k\mathbf{k}:

    (3+λ)i+(−1+2λ)j+(1−λ)k=(4−μ)i+(4+μ)j+(1+2μ)k(3 + \lambda)\mathbf{i} + (-1 + 2\lambda)\mathbf{j} + (1 - \lambda)\mathbf{k} = (4 - \mu)\mathbf{i} + (4 + \mu)\mathbf{j} + (1 + 2\mu)\mathbf{k}
  2. Equate the coefficients of i\mathbf{i}, j\mathbf{j}, and k\mathbf{k} to form a system of linear equations.

    For i\mathbf{i}:

    3+λ=4−μ3 + \lambda = 4 - \mu λ+μ=1(Equation 1)\lambda + \mu = 1 \quad \text{(Equation 1)}

    For j\mathbf{j}:

    −1+2λ=4+μ-1 + 2\lambda = 4 + \mu 2λ−μ=5(Equation 2)2\lambda - \mu = 5 \quad \text{(Equation 2)}

    For k\mathbf{k}:

    1−λ=1+2μ1 - \lambda = 1 + 2\mu −λ−2μ=0-\lambda - 2\mu = 0 λ+2μ=0(Equation 3)\lambda + 2\mu = 0 \quad \text{(Equation 3)}
  3. Solve the system of equations for λ\lambda and μ\mu.

    We can use Equation 1 and Equation 2.
    Add Equation 1 and Equation 2:

    (λ+μ)+(2λ−μ)=1+5(\lambda + \mu) + (2\lambda - \mu) = 1 + 5 3λ=63\lambda = 6 λ=2\lambda = 2

    Substitute λ=2\lambda = 2 into Equation 1:

    2+μ=12 + \mu = 1 μ=1−2\mu = 1 - 2 μ=−1\mu = -1
  4. Verify the values of λ\lambda and μ\mu using Equation 3.

    Substitute λ=2\lambda = 2 and μ=−1\mu = -1 into Equation 3:

    λ+2μ=0\lambda + 2\mu = 0 2+2(−1)=02 + 2(-1) = 0 2−2=02 - 2 = 0 0=00 = 0

    The values satisfy all three equations, confirming that the lines intersect at these values.

    The values are λ=2\lambda = 2 and μ=−1\mu = -1.

    Comparing this with the given options:
    A λ=2\lambda = 2 and μ=1\mu = 1
    B λ=2\lambda = 2 and μ=−1\mu = -1
    C λ=−2\lambda = -2 and μ=−1\mu = -1
    D λ=−2\lambda = -2 and μ=1\mu = 1

    The correct option is B.

    The final answer is B\boxed{\text{B}}.

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