That is the furthest it could be simplified unless you meant to write the equation as x-(x-y)/2*(x+y)/4 than in that case you would use the rule a/b*c/d=ac/bd.
So then you would simplify x-[tex]\frac{(x-y)}{2}[/tex]*[tex]\frac{(x+y)} {4}[/tex] to:
x-[tex]\frac{(x-y)(x+y)}{8}[/tex]
