Question

$\cos 50^{\circ }50^{\prime }\cos 9^{\circ }10^{\prime }-\sin 50^{\circ }50^{\prime }\sin 9^{\circ }10^{\prime }=$

• A. 0
• B. $\frac{1}{2}$
• C. 1
• D. $\frac{\sqrt{3}}{2}$

Answer 1

Answer: (B)

Use $\cos A\cos B-\sin A\sin B=\cos (A+B)$.