The question is incomplete, I will however explain, with an illustration, how to determine the center and radius of a circle.
Explanation:
The standard equation of a circle is given as:
(x - a)² + (y - b)² = r² ........................(1)
Where (a, b) is the center of the circle, and r is the radius.
An expression can be given for us to find the center and the radius of the circle.
Suppose we were given the expression:
x² + y² - 10x + 4y - 7 = 0.....................(2)
To find the center and the radius, it is left for us to rewrite (2) in the form of (1).
Rearranging (2), we have
(x² - 10x) + (y² + 4y) = 7
Completing the squares of each bracket
(x² - 10x + 25 - 25) + (y² + 4y + 4 - 4) = 7
(x² - 10x + 25) + (y² + 4y + 4) - 25 - 4 = 7
(x² - 10x + 25) + (y² + 4y + 4) - 29 = 7
(x - 5)² + (y + 2)² = 7 + 29
(x - 5)² + (y + 2)² = 36
Or
(x - 5)² + (y + 2)² = 6² .....................(3)
Comparing (3) with one, we see that
a = 5, b = -2, and r = 6
Therefore it is a circle centered at (5, -2) with a 6 unit radius.