Step 1 :We are given that \(\sin \theta = \frac{2}{5}\) and \(0 < \theta < \frac{\pi}{2}\). We are asked to find the value of \(\sin (2 \theta)\).
Step 2 :We can use the double angle formula for sine, which is \(\sin (2 \theta) = 2 \sin \theta \cos \theta\). However, we only know the value of \(\sin \theta\), not \(\cos \theta\).
Step 3 :We can find \(\cos \theta\) using the Pythagorean identity \(\sin^2 \theta + \cos^2 \theta = 1\). Solving for \(\cos \theta\), we get \(\cos \theta = \sqrt{1 - \sin^2 \theta} = \sqrt{1 - \left(\frac{2}{5}\right)^2} = \sqrt{1 - \frac{4}{25}} = \sqrt{\frac{21}{25}} = \frac{\sqrt{21}}{5}\).
Step 4 :Now that we have the value of \(\cos \theta\), we can substitute it into the double angle formula to find \(\sin (2 \theta)\). Substituting \(\sin \theta = \frac{2}{5}\) and \(\cos \theta = \frac{\sqrt{21}}{5}\) into the formula, we get \(\sin (2 \theta) = 2 \cdot \frac{2}{5} \cdot \frac{\sqrt{21}}{5} = \frac{4\sqrt{21}}{25}\).
Step 5 :Final Answer: \(\sin (2 \theta) = \boxed{\frac{4\sqrt{21}}{25}}\)