A=4X^2-4XY+Y^2,....(1)B=X^2+XY-5Y^2........(2)........(2)*4+,....(1)A+4B=8X^2-19Y^28X^2-19Y^2=A+4B4X^2-3XY=1，X^2-4Y^2=-3A+B=4X^2-4XY+Y^2+X^2+XY-5Y^2=5X^2-3XY-4Y^2=(4X^2-3XY)+(X^2-4Y^2)=1-3= -2
