Question

Помогите пожалуйста решить 7 и 9 пример

Answer 1

$\displaystyle\bf\\7)\\\\Cos10^\circ Cos35^\circ-Sin35^\circ Sin10^\circ=Cos(35^\circ+10^\circ)=\\\\=Cos45^\circ=\frac{\sqrt{2} }{2} \\\\\\9)\\\\Sin22,5^\circ Sin22,5^\circ-Cos22,5^\circ Cos22,5^\circ=- Cos(22,5^\circ+22,5^\circ)=\\\\=-Cos45^\circ=-\frac{\sqrt{2} }{2}$