Given equation of circle is x2 + y2=a2 and equation of chord x+ y=a For point of intersection eliminate y, we get x2 + (a−x)2=a2 ⇒ x=0, a Hence intersection point A(0,a) and B(0, a) Now circle with AB as diameter is (x−0)(x−a)+( y−a)( y−0)=0 ⇒ x2 + y2 − ax−ay=0