SOLUTION: I need help to prove the identity: Sin10y-sin4yścos4y+cos10y=tan3y

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Question 926756: I need help to prove the identity:
Sin10y-sin4yścos4y+cos10y=tan3y

Answer by Edwin McCravy(20059)   (Show Source): You can put this solution on YOUR website!
To prove the identity:



The average of 10y and 4y is 7y, so write 10y as 7y+3y and 4y as 7y-3y




Use the double angle formulas for sin(A±B) and cos(A±B):

















Edwin
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