Question

What is the equation of a circle whose center is at the origin and whose radius is 9?

Answer 1

x ^2 + y^ 2 = 9

Answer 2

The general equation of a circle is given by;

`(x-a)^(2) + (y-b)^(2) = r^(2)`
Where (a, b) is the centre of the circle and r is the radius.

For the given circle, centre is (0,0) and r=9
This

`(x-0)^(2) + (y-0)^(2) = 9^(2)`

`x^(2) + y^(2) = 9^(2)`