Question

The equation x2-8x+y2=9 defines a circle in the xy-coordinate plane. What is the radius of the circle

Answer 1

x² - 8x + y² = 9
(x² - 8x + 16) + y² = 9 + 16
(x - 4)² + y² = 25
(x - 4)² + y² = 5²

he radius is equal to 5.

Answer 2

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)