Vector Algebra
NCERT Class 12
CBSE
Grade 12
Question:
If $\theta$ is the angle between two non-zero vectors $\vec{a}$ and $\vec{b}$, then $\vec{a} \cdot \vec{b} \ge 0$ when:
(a) $0 \le \theta \le \dfrac{\pi}{2}$
(b) $0 < \theta < \pi$
(c) $\dfrac{\pi}{2} \le \theta \le \pi$
(d) $0 \le \theta \le \pi$
Step-by-Step Solution
$\cos\theta \ge 0 \iff 0 \le \theta \le \pi/2$. [1.0 Mark]
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🎯 Official CBSE Marking Scheme:
Selecting $0 \le \theta \le \pi/2$: 1.0 Mark
Correct Answer: $0 \le \theta \le \dfrac{\pi}{2}$
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