Obtain the differential equation of all circles of radius `rdot`

Explanation

To obtain the differential equation of all circles of radius \( r \), we will follow these steps:

### Step 1: Write the general equation of a circle
The general equation of a circle with center \( (a, b) \) and radius \( r \) is given by:
\[ (x - a)^2 + (y - b)^2 = r^2 \]

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