Sin(x)+sin(3x)+cos(x)+cos(3x)=0[sin(x)+sin(3x)]+[cos(x)+cos(3x)]=02sin((3x+x)/2)*cos((3x-x)/2)+2cos((3x+x)/2)*cos((3x-x)/2)=02sin(2x)*cos(x)+2cos(2x)*cos(x)=02*cos(x)*(sin(2x)+cos(2x))=01)
cos(x)=0x=pi/2+pi*n(2)sin(2x)+cos(2x)=0sin(2x)=-cos(2x)sin(2x)/cos(2x)=-cos(2x)/cos(2x)tg(2x)=-12x=arctg(-1)+pi*n2x-3*pi/4+pi*nx=3pi/8+pi*n/2