Answer
$\dfrac{1}{2}$
Work Step by Step
$\because \sin{(\theta+ 360^{\circ} k)} = \sin{\theta}$
$\therefore \sin{390^{\circ}} = \sin{(30^{\circ}+360^{\circ})} = \sin{30^{\circ}}$
$\sin{30^{\circ}} = \boxed{\dfrac{1}{2}}$
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