Question 177042
{{{matrix(7,3,

-Sin^2x-Sin^2y+1,"=",Cos(x+y)Cos(x-y),
              "","=",(Cos(x)Cox(y)-Sin(x)Sin(y))(Cos(x)Cox(y)+Sin(x)Sin(y)),
              "","=",Cos^2x*Cos^2y-Sin^2x*Sin^2y,
              "","=",(1-Sin^2x)(1-Sin^2y)-Sin^2x*Sin^2y,
              "","=",1-Sin^2y-Sin^2x+Sin^2x*Sin^2y-Sin^2x*Sin^2y,
              "","=",1-Sin^2y-Sin^2x,
              "","=",-Sin^2x-Sin^2y+1)}}} 
<pre><font size = 4 color = "indigo"><b>
Edwin</pre>