Which of the following quadratic equations has no integer solution?
x2−y2=1x^2 - y^2 = 1x2−y2=1
x2−y2=2x^2 - y^2 = 2x2−y2=2
x2+y2=3x^2 + y^2 = 3x2+y2=3
x2−y2=4x^2 - y^2 = 4x2−y2=4