Class CBSE Class 12 Mathematics Three Dimensional Geometry Q #883
COMPETENCY BASED
APPLY
5 Marks 2023 LA
35. (a) Show that the following lines do not intersect each other : $\frac{x-1}{3}=\frac{y+1}{2}=\frac{z-1}{5};\frac{x+2}{4}=\frac{y-1}{3}=\frac{z+1}{-2}$

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Step-by-Step Solution

  1. Write the equations of the lines in parametric form:<\/strong><\/p>

    Line 1: \(\frac{x-1}{3}=\frac{y+1}{2}=\frac{z-1}{5} = \lambda\)
    \(x = 3\lambda + 1\), \(y = 2\lambda - 1\), \(z = 5\lambda + 1\)

    Line 2: \(\frac{x+2}{4}=\frac{y-1}{3}=\frac{z+1}{-2} = \mu\)
    \(x = 4\mu - 2\), \(y = 3\mu + 1\), \(z = -2\mu - 1\)

  2. Equate the coordinates to find the point of intersection (if it exists):<\/strong><\/p>

    \(3\lambda + 1 = 4\mu - 2\) (1)
    \(2\lambda - 1 = 3\mu + 1\) (2)
    \(5\lambda + 1 = -2\mu - 1\) (3)

  3. Solve equations (1) and (2) for \(\lambda\) and \(\mu\):<\/strong><\/p>

    From (1): \(3\lambda - 4\mu = -3\) (4)
    From (2): \(2\lambda - 3\mu = 2\) (5)

    Multiply (4) by 2 and (5) by 3:
    \(6\lambda - 8\mu = -6\) (6)
    \(6\lambda - 9\mu = 6\) (7)

    Subtract (6) from (7):
    \(-\mu = 12\)
    \(\mu = -12\)

    Substitute \(\mu = -12\) into (5):
    \(2\lambda - 3(-12) = 2\)
    \(2\lambda + 36 = 2\)
    \(2\lambda = -34\)
    \(\lambda = -17\)

  4. Check if these values of \(\lambda\) and \(\mu\) satisfy equation (3):<\/strong><\/p>

    Substitute \(\lambda = -17\) and \(\mu = -12\) into (3):
    \(5(-17) + 1 = -2(-12) - 1\)
    \(-85 + 1 = 24 - 1\)
    \(-84 = 23\)

    This is not true, so the lines do not intersect.

Correct Answer: The lines do not intersect.<\/strong>

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because it requires students to apply their understanding of the conditions for intersection of lines in 3D space to determine whether the given lines intersect.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure to check if two lines intersect, involving setting up equations and solving them.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. The question assesses the student's ability to apply the concepts of 3D geometry to a specific problem, rather than simply recalling definitions or formulas.