The small circle has equation #x^(2)+y^(2)-2x-4y-4=0#. The great circle equation have the same radius with the diameter of the small circle is ...?
If I understand your question correctly, the large circle has a radius of 6. If the two circles share the same center, the equation of the large circle is
Get the equation of the circle from general form to standard form by completing the two squares:
Rearrange terms, move constant to other side of the equation:
Complete the square for the
This is the standard form of the circle.