Cho

Câu hỏi: Cho $\alpha , \beta$ thỏa mãn $\sin \alpha +\hspace{0.17em}\sin \beta = \frac{\sqrt{2}}{2}; \cos \alpha +\hspace{0.17em}\cos \beta = \frac{\sqrt{6}}{2}$. Tính $\cos \left(\alpha -\beta \right)$.

A. $\cos \left(\alpha -\beta \right)=0$

B. $\cos \left(\alpha -\beta \right)=\frac{\sqrt{2}}{2}$

C. $\cos \left(\alpha -\beta \right)=\frac{\sqrt{3}}{2}$

D. $\cos \left(\alpha -\beta \right)=\frac{1}{2}$