1. 

   sunriso New Member

   Докажите тождества1)3cos 2a - sin^2a - cos^2a = 2cos 2a
   2)sin5a - sin 3a / 2 cos 4a = sin a

    

   sunriso, 20 фев 2010

   #1
2. 

   Вальт New Member

   1)3cos 2a - sin^2a - cos^2a = 3cos2a-(cos^2a-sin^2a)=3cos2a-cos2a=2cos 2a
   cos2a=cos^a-sin^2a
   
   2)sin5a - sin 3a / 2 cos 4a = (2sin(5a-3a)/2)*cos(5a+3a)/2)/2cos4a = 2sina*cos4a/2cos4a= sin a
   sina-sinb=2sin(a-b)/2*cos(a+b)/2

    

   Вальт, 20 фев 2010

   #2