Usin sum, difference, and double-angle identities

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January 2nd 2013, 09:56 AM
alejandro

Usin sum, difference, and double-angle identities

Express cos(pi/6)cos(2pi/3)+sin(pi/6)sin(2pi/3) as a single trigonometric expression
January 2nd 2013, 09:59 AM
emakarov

Re: Usin sum, difference, and double-angle identities

Why don't you follow the hint in the title of the thread?
January 2nd 2013, 03:49 PM
Soroban

Re: Usin sum, difference, and double-angle identities

Hello, alejandro!

Quote:

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

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

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