X^3+X^2Y-XY^2-Y^3=0
X^2(X+Y)-Y^2(X+Y)=0
(X^2-Y^2)(X+Y)=0
(X-Y)(X+Y)^2=0
X=Y
该矩形是正方形
边长:28÷4=7cm
面积:7*7=49cm^2