Answer:
5 cm
Explanation:
The general form of the equation of a circle may be given as
(x - a)² + (y - b)² = c²
where c is the radius, a and b are the coordinates of the center of the circle along the x and y axis.
Given the circle
x2-8x+y2=9
To make it similar to the general form
x2-8x + 16 +y2=9 + 16
(x - 4)²+y²= 25
(x - 4)²+y²= 5²
comparing with the general form stated above,
c = 5cm (the radius)