The orbit of the center of a circle tangent to both circles x ^ 2 + y ^ 2 = 1 and x ^ 2 + y ^ 2-8x + 7 = 0 is?

The orbit of the center of a circle tangent to both circles x ^ 2 + y ^ 2 = 1 and x ^ 2 + y ^ 2-8x + 7 = 0 is?

Circle 1, radius 1, center a (0,0), circle 2 (x-4) ^ 2 + y ^ 2 = 9, radius 3, center B (4,0) are easy to draw, and two circles are circumscribed. Let the center C (x, y), radius r be circumscribed with both circles: AC ^ 2 = x ^ 2 + y ^ 2 = (1 + R) ^ 2BC ^ 2 = (x-4) ^ 2 + y ^ 2 = (3 + R) ^ 2bc-ac = 2C