Chứng minh x^2+y^2+2xy-1/x^2-y^2+2x+1=x+y-1/x-y+1

x2+y2+2xy−1x2−y2+2x+1=x+y−1x−y+1

x2+y2+2xy−1x−y+1=x+y−1x+y+1x−y+1

x2−y2+2x+1x+y−1=x+1−yx+1+yx+y−1