cos2x*cosx=cos2,5x*cos0,5x
Буду благодарна)))

1/2(cosx+cos3x)=1/2(cos2x+cos3x)cosx+cos3x=cos2x+cos3xcosx-cos2x=0-2sin(3x/2)sin(x/2)=0sin(3x/2)=0⇒3x/2=πn⇒x=2πn/3sin(x/2)=0⇒x/2=πn⇒x=2πn