Class CBSE Class 12 Mathematics Three Dimensional Geometry Q #664
KNOWLEDGE BASED
APPLY
1 Marks 2024 AISSCE(Board Exam) 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:
(A) 0
(B) \(\frac{\pi}{4}\)
(C) \(\frac{\pi}{2}\)
(D) \(\pi\)
Correct Answer: C

AI Tutor Explanation

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Step-by-Step Solution

  1. Let the angles made by the line with the x, y, and z axes be \(\alpha\), \(\beta\), and \(\gamma\) respectively.
  2. Given that \(\alpha = \frac{\pi}{4}\) and \(\gamma = \frac{\pi}{4}\). We need to find \(\beta\).
  3. We know that \(\cos^2{\alpha} + \cos^2{\beta} + \cos^2{\gamma} = 1\).
  4. Substituting the given values, we have \(\cos^2{\frac{\pi}{4}} + \cos^2{\beta} + \cos^2{\frac{\pi}{4}} = 1\).
  5. Since \(\cos{\frac{\pi}{4}} = \frac{1}{\sqrt{2}}\), we get \(\left(\frac{1}{\sqrt{2}}\right)^2 + \cos^2{\beta} + \left(\frac{1}{\sqrt{2}}\right)^2 = 1\).
  6. This simplifies to \(\frac{1}{2} + \cos^2{\beta} + \frac{1}{2} = 1\).
  7. Therefore, \(\cos^2{\beta} = 1 - \frac{1}{2} - \frac{1}{2} = 0\).
  8. So, \(\cos{\beta} = 0\).
  9. Thus, \(\beta = \frac{\pi}{2}\).

Correct Answer: \(\frac{\pi}{2}\)<\/strong>

AI Suggestion: Option C

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply the formula relating direction cosines to find the unknown angle.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to execute a procedure, namely using the relationship between direction cosines to calculate the angle with the y-axis.
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 from the textbook regarding direction cosines and angles made by a line with coordinate axes.