Answer:
The radius of the given equation is 2 .
Explanation:
The equation of a circle whose center (h, k) and radius is r,
(x - h)² + (y - k)² = r² ..............................(i)
Here given that-
x² + y² + 21 = 10 x
x² - 10 x + y² + 21 = 0
( To making perfect square, add and subtract 25 ) -
x² - 10 x + 25 - 25 + y² + 21 = 0
(x² - 10 x + 25) + y² -4 =0
[As we know that -
(x - 5)² = x² - 10 x + 25]
(x - 5 )² + y² = 4
(x - 5)² + (y - 0)² = 4
(x - 5 )² + (y- 0)² = 2² ................................(ii)
On comparing equation (i) and(ii)-
r = 2
Hence the radius of the given equation is 2 and center is ( 5, 0).