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Use an Addition or Subtraction Formula to find the exact value of the expression, as demonstrated in Example 1.

cos

(5π/

12)

 Dec 4, 2019
 #1
avatar+106539 
+1

cos ( 5 pi  /12)   =

 

It is easiest to convert   the radians to degrees....so

 

5pi/ 12  * 180  /pi   =

 

(5/12) (180)  =   75°

 

So

 

cos  (75°)   =   

 

cos (30  + 45)  =

 

cos30*cos45  - sin 30 *sin 45  =

 

( √3/2 ) (  √2/ 2)   -  (1/2) ( √2/2)  =

 

 √6/4  -  √2/4  =

 

 √6 -  √2

_______

    4

 

 

cool cool cool

 Dec 4, 2019

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