SOLUTION: exact value of cos pi/12 cos pi/6 - sin pi/12 sin pi/6

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Question 969742: exact value of
cos pi/12 cos pi/6 - sin pi/12 sin pi/6
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
You need to know three things:

1. The formula you need is:

cos%28alpha%29cos%28beta%29-sin%28alpha%29sin%28beta%29%22%22=%22%22cos%28alpha%2Bbeta%29

Substitute pi%2F12 for alpha and pi%2F6 for beta in that
formula.

2. You need to know how to add the two fractions you'll have in the right side:

pi%2F12%2Bpi%2F6 by getting a common denominator of 12, and reduce it.

3. Finally you need to know the trig ratios for the special angles:

   |  p/6 |  p/4 | p/3  
----------------------      
sin|  1/2 | √2/2 |√3/2    
---|------|------|----
cos| √3/2 | √2/2 | 1/2

Good luck.  Need any more help?  If so, ask me in the thank-you note form below.
I'll get back to you.

Edwin