Q.If \( \tan\left(\cfrac{\pi}{2} - \cfrac{\alpha}{2}\right) = \sqrt{3} \), then what is the value of \( \cos\alpha \)? (a) \(\cfrac{1}{2}\) (b) \(\cfrac{\sqrt3}{2}\) (c) \(\cfrac{1}{\sqrt2}\) (d) 1
Answer: A
Given: \[ \tan\left(\frac{\pi}{2} - \frac{\alpha}{2}\right) = \sqrt{3} \] Then, \[ \tan\left(\frac{\pi}{2} - \frac{\alpha}{2}\right) = \tan\left(\frac{\pi}{3}\right) \] So, \[ \frac{\pi}{2} - \frac{\alpha}{2} = \frac{\pi}{3} \] Therefore, \[ -\frac{\alpha}{2} = \frac{\pi}{3} - \frac{\pi}{2} \] Or, \[ \frac{\alpha}{2} = \frac{\pi}{2} - \frac{\pi}{3} \] \[ \frac{\alpha}{2} = \frac{3\pi - 2\pi}{6} = \frac{\pi}{6} \] So, \[ \alpha = \frac{\pi}{3} \] Hence, \[ \cos\alpha = \cos\left(\frac{\pi}{3}\right) = \frac{1}{2} \]
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