(0,75х-0,25у)^2-(0,25х+0,75у)^2

[latex](0.75x-0.25y)^2-(0.25x+0.75y)^2= \\ ((0.75x-0.25y)-(0.25x+0.75y)((0.75x-0.25y)+(0.25x+0.75y))= \\ (0.75x-0.25y-0.25x-0.75y)(0.75x-0.25y+0.25x+0.75y)= \\ -0.5x*1.5y=-0.75xy[/latex]