Question 1048795
<pre><b>    
{{{cos(A-B)}}}{{{""=""}}}{{{cos(A)cos(B)+sin(A)sin(B)}}}
{{{cos(A+B)}}}{{{""=""}}}{{{cos(A)cos(B)-sin(A)sin(B)}}}

Subtract the 2nd equation from the 1st:

{{{cos(A-B) - cos(A+B)}}}{{{""=""}}}{{{2sin(A)sin(B)}}}

Multiply both sides by 1/2

{{{expr(1/2)(cos(A-B)^"" - cos(A+B))}}}{{{""=""}}}{{{sin(A)sin(B)}}}

{{{sin(A)sin(B)}}}{{{""=""}}}{{{expr(1/2)(cos(A-B)^"" - cos(A+B))}}}

Let A = x and B = x-y

{{{sin(x)sin(x-y)}}}{{{""=""}}}{{{expr(1/2)(cos(x-(x-y)^"")^"" - cos(x+(x-y)^""))}}}

{{{sin(x)sin(x-y)}}}{{{""=""}}}{{{expr(1/2)(cos(x-x+y^"")^"" - cos(x+x-y^""))}}}

{{{sin(x)sin(x-y)}}}{{{""=""}}}{{{expr(1/2)(cos(y^"")^"" - cos(2x-y^""))}}}

That's ONE-HALF the difference of two cosines, which may be what
you want.  If not let me know in the thank-you note form below,
and I'll try to get rid of the ONE-HALF.

Edwin</pre>