SOLUTION: coul you help me about this?!? Prove the identity {{{Cos^2(2y)-4Sin^2(y)Cos^2(y)=Cos(4y)}}}

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Question 203947: coul you help me about this?!?
Prove the identity
Cos%5E2%282y%29-4Sin%5E2%28y%29Cos%5E2%28y%29=Cos%284y%29
Answer by Edwin McCravy(20065) About Me  (Show Source):
You can put this solution on YOUR website!


        Cos%5E2%282y%29-4Sin%5E2%28y%29Cos%5E2%28y%29=Cos%284y%29

Work with the right side:
                          Cos%284y%29 

                          Cos%282%282y%29%29

                          Cos%5E2%282y%29-Sin%5E2%282y%29

                          Cos%5E2%282y%29-%28Sin%282y%29%29%5E2
               
                          Cos%5E2%282y%29-%282Sin%28y%29Cos%28y%29%29%5E2
    
                          Cos%5E2%282y%29-2%5E2Sin%5E2%28y%29Cos%5E2%28y%29 

                          Cos%5E2%282y%29-4Sin%5E2%28y%29Cos%5E2%28y%29

Edwin