The equation of first circle is, x2+y2−36=0 The equation of second circle is, x2+y2+kx−4k−36=0 since, both the circles are intersecting orthogonally, then −4k−36−36=0 k=−18 The equation of the required circle is expressed as, x2+y2+(−18)x−4(−18)−36=0 x2+y2 - 18x + 36 = 0