Question

помогите пожалуйста​

Answer 1

$cos3x-cosx=0<=>-2sin2xsinx=0<=>sin2xsinx=0\\cos3x+cosx=0<=>2cos2xcosx=0<=>cos2xcosx=0\\sin3x-sinx=0<=>2cos2xsinx=0<=>cos2xsinx=0\\sin5x+sinx=0<=>2sin3xcos2x=0<=>sin3xcos2x=0$

Использовал формулы:

$cosx-cosy=-2sin(\frac{x+y}{2} )sin(\frac{x-y}{2} )\\cosx+cosy=2cos(\frac{x+y}{2} )cos(\frac{x-y}{2} )\\sinx-siny=2cos(\frac{x+y}{2})sin(\frac{x-y}{2} )\\sinx+siny=2sin(\frac{x+y}{2})cos(\frac{x-y}{2} )$