Answer
$1$
Work Step by Step
The sine is an odd function so
$\sin{(-\theta)} = - \sin{\theta}$
Thus,
$\sin{\left(- \dfrac{ 3\pi}{2} \right) } = - \sin{\left( \dfrac{ 3 \pi}{2} \right) } = -(-1)=\boxed{1}$
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