The given equation of circle is x2+y2 – 4x – 8y – 45 = 0
∴ (x2–4x)+(y2–8y) = 45
⇒ [x2 – 4x + (2)2] + [y2 – 8y + (4)2] = 45 + (2)2+(4)2
⇒ (x–2)2+(y–4)2 = 45 + 4 + 16 ⇒ (x–2)2+(y–4)2 = 65
⇒ (x–2)2+(y–4)2 = (√65)2
Comparing it with (x–h)2+(y–k)2 = r2, we have h = 2, k = 4 and r = 65.
Thus co-ordinates of the centre are (2, 4) and radius is 65.