Question

Помогите решить ........................

Answer 1

$3)\sqrt{2}Cos(\alpha -\beta)=\sqrt{2}(Cos\alpha Cos\beta+Sin\alpha Sin\beta)=\sqrt{2}( \frac{1}{2}-\frac{1}{2})=0\\\\4)3Cos(\alpha+\beta)=3(Cos\alpha Cos\beta-Sin\alpha Sin\beta)=3(-\frac{1}{2}+\frac{1}{2})=0$