SOLUTION: Please help me answer this!! Use the identity cos(α+β)= cosαcosβ-sinαsinβ to find the value of cos 7pi/12 Please reply soon and Thaank you in

Algebra ->  Trigonometry-basics -> SOLUTION: Please help me answer this!! Use the identity cos(α+β)= cosαcosβ-sinαsinβ to find the value of cos 7pi/12 Please reply soon and Thaank you in      Log On


   

Question 773663: Please help me answer this!!
Use the identity cos(α+β)= cosαcosβ-sinαsinβ to find the value of cos 7pi/12

Please reply soon and Thaank you in advance!!
Answer by ramkikk66(644) About Me  (Show Source):
You can put this solution on YOUR website!
7%2Api%2F12+=+pi%2F3+%2B+pi%2F4

pi/4 = 45 deg. sin+%28pi%2F4%29+=+cos%28pi%2F4%29+=+1%2Fsqrt%282%29
pi/3 = 60 deg. sin+%28pi%2F3%29+=+sqrt%283%29%2F2 and cos%28pi%2F3%29+=+1%2F2

So  =
%281+-+sqrt%283%29%29%2F%282%2Asqrt%282%29%29
Hope you got it :)