Объяснение:
1)cos(x+1)cos(x-1)=1/2(cos(x+1-x+1)+c0s(x+1+x-1))=1/2(cos2+cos2x)
2)sin(m+n)sin(m-n)=1/2(cos(m+n-m+n)-cos(m+n+m-n))=1/2(cos2n-cos2m);
3)sin(1-x)·cos(1-2x)=1/2(sin(1-x-1+2x)+sin(1-x+1-2x))=1/2(sinx+sin(2-3x)).
