SOLUTION: Use a sum or difference formula to find the exact value of the following.
cos(5pi/7)cos(13pi/28) + sin(5pi/7)sin(13pi/28) =
Algebra ->
Trigonometry-basics
-> SOLUTION: Use a sum or difference formula to find the exact value of the following.
cos(5pi/7)cos(13pi/28) + sin(5pi/7)sin(13pi/28) =
Log On
Question 888776: Use a sum or difference formula to find the exact value of the following.
cos(5pi/7)cos(13pi/28) + sin(5pi/7)sin(13pi/28) = Answer by lwsshak3(11628) (Show Source):
You can put this solution on YOUR website! Use a sum or difference formula to find the exact value of the following.
cos(5pi/7)cos(13pi/28) + sin(5pi/7)sin(13pi/28)
***
Identity: cos(x-y)=cosx*cosy+sinx*siny
cos(5pi/7)cos(13pi/28) + sin(5pi/7)sin(13pi/28)=cos(5π/7-13π/8)=cos(40π/56-91π/56)=cos(-51π/56)
(