The trajectory equation of the center of a moving circle which is circumscribed with the circle x ^ 2; + y ^ 2; = 1 and tangent to the Y axis is?

The trajectory equation of the center of a moving circle which is circumscribed with the circle x ^ 2; + y ^ 2; = 1 and tangent to the Y axis is?

Let the center point of the moving circle be (a, b)
When b > 0, because the moving circle and the circle (x ^ 2; + y ^ 2; = 1) are circumscribed and tangent to the Y axis, then
(b+1)^2=a^2＋b^2
That is, a ^ 2-2b-1 = 0
When B

If the moving circle with radius 1 is tangent to the circle x2 + y2 = 4, the trajectory equation of the center of the moving circle is______ ．

Let the coordinates of the center of the moving circle be a (x, y). If two circles are circumscribed, then | Ao | = 1 + 2 = 3, that is, X2 + y2 = 9. If two circles are inscribed, then | Ao | = 2-1 = 1, that is, X2 + y2 = 1. To sum up, the trajectory equation of the center of the moving circle is & nbsp; x2 + y2 = 9, or x2 + y2 = 1, so the answer is: x2 + y2 = 9, or x2 + y2 = 1