Class CBSE Class 12 Mathematics Vector Algebra Q #553
COMPETENCY BASED
APPLY
1 Marks 2024 AISSCE(Board Exam) MCQ SINGLE
The vectors \(\vec{a}=2\hat{i}-\hat{j}+\hat{k}\), \(\vec{b}=\hat{i}-3\hat{j}-5\hat{k}\) and \(\vec{c}=-3\hat{i}+4\hat{j}+4\hat{k}\) represents the sides of
(A) an equilateral triangle
(B) an obtuse-angled triangle
(C) an isosceles triangle
(D) a right-angled triangle

AI Tutor Explanation

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Step-by-Step Solution

Let the sides of the triangle be represented by the vectors \(\vec{a}\), \(\vec{b}\), and \(\vec{c}\).

\(\vec{a} = 2\hat{i} - \hat{j} + \hat{k}\)

\(\vec{b} = \hat{i} - 3\hat{j} - 5\hat{k}\)

\(\vec{c} = -3\hat{i} + 4\hat{j} + 4\hat{k}\)

Find the magnitudes of the vectors:

\(|\vec{a}| = \sqrt{2^2 + (-1)^2 + 1^2} = \sqrt{4 + 1 + 1} = \sqrt{6}\)

\(|\vec{b}| = \sqrt{1^2 + (-3)^2 + (-5)^2} = \sqrt{1 + 9 + 25} = \sqrt{35}\)

\(|\vec{c}| = \sqrt{(-3)^2 + 4^2 + 4^2} = \sqrt{9 + 16 + 16} = \sqrt{41}\)

Check if the triangle is right-angled by verifying the Pythagorean theorem:

\(|\vec{a}|^2 + |\vec{b}|^2 = 6 + 35 = 41\)

\(|\vec{c}|^2 = 41\)

Since \(|\vec{a}|^2 + |\vec{b}|^2 = |\vec{c}|^2\), the triangle is right-angled.

Correct Answer: D<\/strong>

AI Suggestion: Option D

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply their knowledge of vectors and triangle properties to determine the type of triangle formed.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure to find the sides of the triangle using vectors and then apply the properties of triangles to classify it.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. The question assesses the student's ability to apply vector concepts to a geometric problem, requiring more than just recalling definitions or formulas.