Question

срочно надо пжжжжжжжж помогитеее​

Answer 1

$\alpha\in2chetverti \Rightarrow Cos\alpha<0\\\\Cos\alpha=-\sqrt{1-Sin^{2}\alpha}=-\sqrt{1-0,2^{2}}=-\sqrt{1-0,04}=-\sqrt{0,96}=-\frac{4\sqrt{6}}{10}=-\frac{2\sqrt{6}}{5}\\\\Sin(\frac{\pi }{4}-\alpha)=Sin\frac{\pi }{4}Cos\alpha-Cos\frac{\pi }{4}Sin\alpha=\frac{\sqrt{2}}{2}*(-\frac{2\sqrt{6}}{5})-\frac{\sqrt{2}}{2}*\frac{1}{5}=-\frac{2\sqrt{3}}{5}-\frac{\sqrt{2}}{10}=-\frac{4\sqrt{3}+\sqrt{2}}{10}$