Question

Математика Срочно .
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Answer 1

$1-\cfrac{2}{\mathrm{tg}\alpha +\mathrm{ctg}\alpha }=1-\cfrac{2}{\cfrac{\sin \alpha }{\cos \alpha }+\cfrac{\cos \alpha }{\sin \alpha }}=1-\cfrac{2}{\cfrac{\sin^2 \alpha +\cos ^2\alpha }{\sin \alpha \cos \alpha }}=1-2\sin \alpha \cos \alpha\\\\\\(\sin\alpha -\cos \alpha )^2=\sin ^2\alpha -2\sin \alpha +\cos^2\alpha =1-2\sin\alpha \cos \alpha$