Which pair (x,y)(x, y)(x,y) satisfies x2−y2=21x^2 - y^2 = 21x2−y2=21?
(5,2)(5, 2)(5,2)
(7,4)(7, 4)(7,4)
(11,10)(11, 10)(11,10)
(6,3)(6, 3)(6,3)