Answer
$0$
Work Step by Step
$sin45^\circ+sin135^\circ+sin225^\circ+sin315^\circ\\ =sin45^\circ+sin(180-45)^\circ+sin(180+45)^\circ+sin(360-45)^\circ\\ =sin45^\circ+sin45^\circ-sin45^\circ-sin45^\circ=0$
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