SOLUTION: usa a sum or difference identity to find the exact value of the expression cos(5pi/12)

Question 1051954: usa a sum or difference identity to find the exact value of the expression cos(5pi/12)
Answer by Edwin McCravy(20055) (Show Source): You can put this solution on YOUR website!

   

 is not a special angle.  We see if we 
can break  into a sum or difference of 
the three special angles , , 
and .

We change the special angles so as to have denominator 12:

, , 

So we see that 

We use the identity: 





Edwin

RELATED QUESTIONS
use an appropriate identity to find the exact value of the expression cos... (answered by stanbon,josgarithmetic)
Find the exact value using a sum or difference identity. Some simplifications may involve (answered by ikleyn)
Use a sum or difference formula to find the exact value of the following.... (answered by lwsshak3)
use sum or difference formula to find exact value of the following:... (answered by Edwin McCravy)
Use the angle sum or difference identity to find the exact value of cos195... (answered by Edwin McCravy)
Find the exact value using a sum or difference identity. cos(165�) (answered by stanbon)
17. find the exact value of cos... (answered by Mathtut)
find the exact value by using a sum or difference identity... (answered by stanbon)
How do I find the cos(5pi/12)?! The question says "Use the sum or difference formula to... (answered by Alan3354,lwsshak3)