Class CBSE Class 12 Mathematics Three Dimensional Geometry Q #670
KNOWLEDGE BASED
APPLY
1 Marks 2024 AISSCE(Board Exam) MCQ SINGLE
If the direction cosines of a line are \(\sqrt{3}k, \sqrt{3}k\), \(\sqrt{3}k,\) then the value of k is:
(A) \(\pm1\)
(B) \(\pm\sqrt{3}\)
(C) \(\pm3\)
(D) \(\pm\frac{1}{3}\)
Correct Answer: D

AI Tutor Explanation

Powered by Gemini

Step-by-Step Solution

Let the direction cosines be \(l, m, n\). We are given that \(l = \sqrt{3}k\), \(m = \sqrt{3}k\), and \(n = \sqrt{3}k\).

We know that the sum of the squares of the direction cosines is equal to 1, i.e., \(l^2 + m^2 + n^2 = 1\).

Substituting the given values, we have:

\((\sqrt{3}k)^2 + (\sqrt{3}k)^2 + (\sqrt{3}k)^2 = 1\)

\(3k^2 + 3k^2 + 3k^2 = 1\)

\(9k^2 = 1\)

\(k^2 = \frac{1}{9}\)

Taking the square root of both sides, we get:

\(k = \pm\sqrt{\frac{1}{9}}\)

\(k = \pm\frac{1}{3}\)

Correct Answer: \(\pm\frac{1}{3}\)

AI Suggestion: Option D

AI generated content. Review strictly for academic accuracy.

Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply the formula relating direction cosines to find the value of k.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure (using the identity \(l^2 + m^2 + n^2 = 1\)) to calculate the value of k.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's understanding and application of a standard formula related to direction cosines, which is a core concept covered in the textbook.

More from this Chapter

LA
Find the vector and the Cartesian equations of a line passing through the point (1,2,-4) and parallel to the line joining the points A(3,3,-5) and B(1,0,-11). Hence, find the distance between the two lines. OR Find the equations of the line passing through the points A(1,2,3) and B(3,5,9). Hence, find the coordinates of the points on this line which are at a distance of 14 units from point B.
VSA
If the angle between the lines $\frac{x-5}{\alpha}=\frac{y+2}{-5}=\frac{z+\frac{24}{5}}{\beta}$ and $\frac{x}{1}=\frac{y}{0}=\frac{z}{1}$ is $\frac{\pi}{4}$, find the relation between $\alpha$ and $\beta$.
MCQ_SINGLE
If a line makes an angle of \(\frac{\pi}{4}\) with the positive directions of both x-axis and z-axis, then the angle which it makes with the positive direction of y-axis is:
LA
If the lines $\frac{x-1}{-3}=\frac{y-2}{2k}=\frac{z-3}{2}$ and $\frac{x-1}{3k}=\frac{y-1}{1}=\frac{z-6}{-7}$ are perpendicular to each other, find the value of k and hence write the vector equation of a line perpendicular to these two lines and passing through the point (3, -4, 7).
SA
Find the coordinates of the foot of the perpendicular drawn from the point $P(0, 2, 3)$ to the line:$$\frac{x+3}{5} = \frac{y-1}{2} = \frac{z+4}{3}$$ OR (b) Three vectors $\vec{a}$, $\vec{b}$, and $\vec{c}$ satisfy the condition $\vec{a} + \vec{b} + \vec{c} = \vec{0}$. Evaluate the quantity $\mu = \vec{a} \cdot \vec{b} + \vec{b} \cdot \vec{c} + \vec{c} \cdot \vec{a}$, if $|\vec{a}| = 3$, $|\vec{b}| = 4$, and $|\vec{c}| = 2$.
View All Questions