<span>сos(x-y)=1 </span><span>вычитаете </span><span>cos(x+y)=-1/2 </span><span>x-y=2пк </span><span>x+y=2п/3+ 2пm </span><span>x-y=2пк </span><span>x+y=-2п/3+2пm</span>