Class CBSE Class 12 Mathematics Three Dimensional Geometry Q #1413
COMPETENCY BASED
UNDERSTAND
3 Marks 2025 AISSCE(Board Exam) SA
Find the distance of the point $(-1, -5, -10)$ from the point of intersection of the lines $\frac{x-1}{2}=\frac{y-2}{3}=\frac{z-3}{4}$ and $\frac{x-4}{5}=\frac{y-1}{2}=z$.

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Detailed Solution

Step 1: Find the general points on both lines

Let's express the general points on both lines using parameters $\lambda$ and $\mu$. Line 1: $\frac{x-1}{2}=\frac{y-2}{3}=\frac{z-3}{4} = \lambda$ $x = 2\lambda + 1, y = 3\lambda + 2, z = 4\lambda + 3$ Line 2: $\frac{x-4}{5}=\frac{y-1}{2}=z = \mu$ $x = 5\mu + 4, y = 2\mu + 1, z = \mu$

Step 2: Equate the coordinates to find the intersection point

For the lines to intersect, the coordinates must be equal at some point. $2\lambda + 1 = 5\mu + 4$ (1) $3\lambda + 2 = 2\mu + 1$ (2) $4\lambda + 3 = \mu$ (3)

Step 3: Solve the system of equations

Substitute (3) into (1) and (2): $2\lambda + 1 = 5(4\lambda + 3) + 4$ $2\lambda + 1 = 20\lambda + 15 + 4$ $18\lambda = -18$ $\lambda = -1$ $3\lambda + 2 = 2(4\lambda + 3) + 1$ $3\lambda + 2 = 8\lambda + 6 + 1$ $5\lambda = -5$ $\lambda = -1$ Now, find $\mu$ using equation (3): $\mu = 4\lambda + 3 = 4(-1) + 3 = -1$

Step 4: Find the intersection point

Using $\lambda = -1$ in the first line's equations: $x = 2(-1) + 1 = -1$ $y = 3(-1) + 2 = -1$ $z = 4(-1) + 3 = -1$ So, the intersection point is $(-1, -1, -1)$.

Step 5: Calculate the distance between the given point and the intersection point

The given point is $(-1, -5, -10)$. The intersection point is $(-1, -1, -1)$. Distance $d = \sqrt{(-1 - (-1))^2 + (-5 - (-1))^2 + (-10 - (-1))^2}$ $d = \sqrt{(0)^2 + (-4)^2 + (-9)^2}$ $d = \sqrt{0 + 16 + 81}$ $d = \sqrt{97}$

Final Answer: $\sqrt{97}$

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Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because the student needs to understand the concept of lines in 3D space, their parametric representation, and how to find the intersection point. They also need to understand the distance formula in 3D.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to apply a series of well-defined steps: converting lines to parametric form, solving simultaneous equations, and applying the distance formula. These are all procedural skills.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. The question requires the student to apply their knowledge of 3D geometry to solve a problem involving finding the intersection of lines and calculating distances. This goes beyond simple recall and requires application of concepts.