## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$-\sqrt{2}$
The cosecant is an odd function so $\csc{(- \theta)} = - \csc{\theta}$ Thus, $\csc{\left(-\dfrac{\pi}{4} \right)} = - \csc{\left(\dfrac{\pi}{4} \right)} =\boxed{- \sqrt{2}}$