Answer
$1-2\sin \alpha \cos \alpha =1-\sin 2\alpha $
Work Step by Step
$\left( \sin \alpha -\cos \alpha \right) ^{2}=\sin ^{2}\alpha -2\sin \alpha \cos \alpha +\cos ^{2}\alpha =1-2\sin \alpha \cos \alpha =1-\sin 2\alpha $
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