(X+Y)^2=(A+B)^2X^2+2XY+Y^2=A^2+2AB+B^2X^2+2XY+Y^2-4XY+4AB=A^2+2AB+B^2-52(X-Y)^2=A^2+2AB+B^2-52-4AB(X-Y)^2=(A-B)^2-52X-Y=根号下(A-B)^2-52
1
