Class CBSE Class 12 Mathematics Three Dimensional Geometry Q #673
COMPETENCY BASED
APPLY
1 Marks 2025 AISSCE(Board Exam) MCQ SINGLE
The equation of a line parallel to the vector \(3\hat{i}+\hat{j}+2\hat{k}\) and passing through the point \((4, -3, 7)\) is:
(A) \(x=4t+3, y=-3t+1, z=7t+2\)
(B) \(x=3t+4, y=t+3, z=2t+7\)
(C) \(x=3t+4, y=t-3, z=2t+7\)
(D) \(x=3t+4, y=-t+3, z=2t+7\)
Correct Answer: C
Explanation
The vector equation of a line passing through point $\vec{a}$ and parallel to vector $\vec{b}$ is $\vec{r} = \vec{a} + t\vec{b}$.
Here, $\vec{a} = (4, -3, 7)$ and $\vec{b} = (3, 1, 2)$.
So, $(x, y, z) = (4, -3, 7) + t(3, 1, 2) = (4+3t, -3+t, 7+2t)$.
Thus, $x = 3t+4, y = t-3, z = 2t+7$.
This matches Option C.

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Step-by-Step Solution

The equation of a line passing through a point \(\vec{a}\) and parallel to a vector \(\vec{b}\) is given by \(\vec{r} = \vec{a} + t\vec{b}\), where \(t\) is a scalar.

Here, the point is \((4, -3, 7)\), so \(\vec{a} = 4\hat{i} - 3\hat{j} + 7\hat{k}\).

The vector parallel to the line is \(3\hat{i} + \hat{j} + 2\hat{k}\), so \(\vec{b} = 3\hat{i} + \hat{j} + 2\hat{k}\).

Therefore, the equation of the line is \(\vec{r} = (4\hat{i} - 3\hat{j} + 7\hat{k}) + t(3\hat{i} + \hat{j} + 2\hat{k})\).

In component form, this is:

\(x = 4 + 3t\)

\(y = -3 + t\)

\(z = 7 + 2t\)

Rearranging, we get:

\(x = 3t + 4\)

\(y = t - 3\)

\(z = 2t + 7\)

Correct Answer: x=3t+4, y=t-3, z=2t+7

AI Suggestion: Option C

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because it requires students to apply their understanding of vector equations of lines to find the correct parametric equation given a point and a parallel vector.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to apply a specific procedure (forming the equation of a line given a point and a parallel vector) to arrive at the solution.
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 vectors and 3D geometry to solve a specific problem, rather than simply recalling a definition or theorem.