text: # if sinx+sin2x=2then find,cos2x+cos4x
  
  Vinay Arya
  37 Points
  13 years ago
  
  Hi Vishwa Sharma
  
  sinx+sin2x=2
  
  =>sinx+sin2x-2=0
  
  =>(sinx-1)(sinx+2)=0
  
  =>sinx=1 or sinx=-2
  
  We know that sinx cannot be equal to -2.Hence rejaecting sinx=-2
  
  Therefore, sinx=1 =>x=pi/2
  
  cos2x+cos4x=xos2pi/2 + cos4pi/2 =0
  
  Chaitanya Borah
  34 Points
  13 years ago
  
  sinx+sin2x=2
  
  =>sinx=1+1-sin2x
  
  =>sinx=1+cos2x
  
  =>cos2x=sinx-1
  
  now,
  
  cos2x+cos4x
  
  =cos2x+(sinx-1)2
  
  =cos2x+sin2x-2sinx+1
  
  =1-2sinx+1
  
  =2(1-sinx)