Q.If \( \cos^2\theta - \sin^2\theta = \frac{1}{2} \), then what is the value of \( \tan\theta \)? (a) \(-\cfrac{1}{\sqrt3}\) (b) \(\cfrac{1}{3}\) (c) \(\cfrac{1}{\sqrt3}\) (d) \(-\cfrac{1}{3}\)
Answer: C
Given: \( \cos^2\theta - \sin^2\theta = \frac{1}{2} \) — (i) Also, \( \cos^2\theta + \sin^2\theta = 1 \) — (ii) Adding equations (i) and (ii): \( 2\cos^2\theta = \frac{1}{2} + 1 = \frac{3}{2} \) ⇒ \( \cos^2\theta = \frac{3}{4} \) ⇒ \( \sec^2\theta = \frac{4}{3} \) ⇒ \( \sec^2\theta - 1 = \frac{4}{3} - 1 = \frac{1}{3} \) ⇒ \( \tan^2\theta = \frac{1}{3} \) ⇒ \( \tan\theta = \sqrt{\frac{1}{3}} = \frac{1}{\sqrt{3}} \)
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