Question

If $\theta$ is the angle between two vectors $\overrightarrow{a}$ and $\overrightarrow{b}$ , then $\overrightarrow{a}.\overrightarrow{b}\,>\,0$ only if

• A. $0\leq\,\theta\,\leq\,\pi $
• B. $\frac{\pi}{2}\leq\,\theta\,\leq\,\pi $
• C. $0\,\leq\,\theta\,\leq\,\frac{\pi}{2} $
• D. $0\,<\,\theta\,<\,\frac{\pi}{2} $

Answer 1

Answer: (D)

$\vec{d}.\vec{b}=ab\,cos\,\theta > 0$ if $0 < 0 < \frac{\pi}{2} \left[\because cos\,\theta > 0\right]$