Given two diameters of the circle are along the lines x+y=0 and x−y=0. The center of the circle is at their intersection. We have, x−y=0⇒x=y Substitute into x+y=0 : x+x=0⇒2x=0⇒x=0,y=0 Thus, the center is (0,0). Also radius, r=
10
2
=5 the equation of the circle with center (0,0) and radius 5 is x2+y2=52=25