Q.If \(x\) is a real positive number and \(\sin x = \frac{2}{3}\), then what is the value of \(\tan x\)? (a) \(\cfrac{2}{\sqrt5}\) (b) \(\cfrac{\sqrt5}{2}\) (c) \(\sqrt{\cfrac{5}{3}}\) (d) \(\cfrac{\sqrt5}{\sqrt2}\)
Answer: A
\[ \sin x = \frac{2}{3} \] \[ \therefore \sin^2 x = \left(\frac{2}{3}\right)^2 = \frac{4}{9} \] So, \[ 1 - \sin^2 x = 1 - \frac{4}{9} = \frac{5}{9} \] That means, \[ \cos^2 x = \frac{5}{9} \] So, \[ \cos x = \sqrt{\frac{5}{9}} = \frac{\sqrt{5}}{3} \] \[ \therefore \tan x = \frac{\sin x}{\cos x} = \frac{\frac{2}{3}}{\frac{\sqrt{5}}{3}} = \frac{2}{\sqrt{5}} \]
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