#### Answer

$\displaystyle \frac{\sqrt{5}}{5}$

#### Work Step by Step

Letting $A=2\theta, $
we express $\displaystyle \theta=\frac{A}{2},$ whose sine is positive as it terminates in Q.I.
Half-Angle identity:
$\displaystyle \sin\frac{A}{2}=+\sqrt{\frac{1-\cos A}{2}}=\sqrt{\frac{1-0.6}{2}}$
$=\displaystyle \sqrt{0.2}=\sqrt{\frac{1}{5}}=\frac{\sqrt{5}}{5}$