Express cos(pi/6)cos(2pi/3)+sin(pi/6)sin(2pi/3) as a single trigonometric expression
Hello, alejandro!
$\displaystyle \text{Express }\cos\tfrac{\pi}{6}\cos\tfrac{2\pi}{3}+\sin\tfrac{ \pi}{6}\sin\tfrac{2\pi}{3}\,\text{ as a single trigonometric expression.}$
Big hint: .$\displaystyle \cos(A - B) \:=\:\cos A\cos B + \sin A\sin B$