Question

помогите, пожалуйста, с тригонометрией!!

Answer 1

$\displaystyle\bf\\Cos\bigg(\alpha +\frac{7\pi }{12} \bigg)=\frac{3}{5}\\\\\\Cos\bigg(\frac{5\pi }{12} -\alpha \bigg)=Cos\bigg[\pi -\bigg(\frac{7\pi }{12} +\alpha \bigg)\bigg]=-Cos\bigg(\frac{7\pi }{12} +\alpha \bigg)=-\frac{3}{5} \\\\\\Otvet: \ Cos\bigg(\frac{5\pi }{12} -\alpha \bigg)=-\frac{3}{5}$