SOLUTION: Use a sum or difference formula to find the exact value of the following Cos13pie/30 cos2pie/5 - sin13pie/30 sin2pie/5

Algebra ->  Trigonometry-basics -> SOLUTION: Use a sum or difference formula to find the exact value of the following Cos13pie/30 cos2pie/5 - sin13pie/30 sin2pie/5       Log On


   

Question 1036267: Use a sum or difference formula to find the exact value of the following
Cos13pie/30 cos2pie/5 - sin13pie/30 sin2pie/5
Answer by Cromlix(4381) About Me  (Show Source):
You can put this solution on YOUR website!
Hi there,
cos13π/30 cos2π/5 - sin13π/30 sin2π/5
= cos(13π/30 + 2π/5)
Take to common denominator = 30
= cos((13π+12π/30)
= cos(25π/30)
= cos (5π/6)
Hope this helps :-)