Question -
Answer -
The equation of the given circle is x2 + y2 – 4x – 8y –45 = 0.
x2 + y2 – 4x – 8y –45 = 0
⇒ (x2 – 4x) + (y2 – 8y) = 45
⇒ {x2 – 2(x)(2) + 22} + {y2 – 2(y)(4)+ 42} – 4 –16 = 45
⇒ (x – 2)2 + (y –4)2 = 65
⇒ (x – 2)2 + (y –4)2 = 
, which is of the form (x – h)2 + (y – k)2 = r2, where h =2, k = 4, and 
.
Thus,the centre of the given circle is (2, 4), while its radius is
.