Vector Algebra
NCERT Exemplar Class 12
CBSE
Grade 12
Question:
The angle between vectors $\vec{a} = \hat{i} - \hat{j} + \hat{k}$ and $\vec{b} = \hat{i} + \hat{j} - \hat{k}$ is:
(a) $\cos^{-1}(-1/3)$
(b) $\cos^{-1}(1/3)$
(c) $\pi/3$
(d) $\pi/2$
Step-by-Step Solution
cos\theta = (1 - 1 - 1)/(\sqrt{3}\sqrt{3}) = -1/3. [1.0 Mark]
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🎯 Official CBSE Marking Scheme:
Selecting $\cos^{-1}(-1/3)$: 1.0 Mark
Correct Answer: $\cos^{-1}(-1/3)$
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