Express cos(pi/6)cos(2pi/3)+sin(pi/6)sin(2pi/3) as a single trigonometric expression

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- Jan 2nd 2013, 09:56 AMalejandroUsin sum, difference, and double-angle identities
**Express cos(pi/6)cos(2pi/3)+sin(pi/6)sin(2pi/3) as a single trigonometric expression** - Jan 2nd 2013, 09:59 AMemakarovRe: Usin sum, difference, and double-angle identities
Why don't you follow the hint in the title of the thread?

- Jan 2nd 2013, 03:49 PMSorobanRe: Usin sum, difference, and double-angle identities
Hello, alejandro!

Quote:

$\displaystyle \text{Express }\cos\tfrac{\pi}{6}\cos\tfrac{2\pi}{3}+\sin\tfrac{ \pi}{6}\sin\tfrac{2\pi}{3}\,\text{ as a single trigonometric expression.}$

Big hint: .$\displaystyle \cos(A - B) \:=\:\cos A\cos B + \sin A\sin B$