Question

What is the equation of a circle centered at the origin with radius 13?

Answer 1

It is `x^2+y^2-169=0`.

Explanation:

The circle you are looking fore is composed by all the points with a distance from the origin of `13`/ The distance of a point from the center is

`d=sqrt(x^2+y^2)` and this distance has to be `13`, so

`13=sqrt(x^2+y^2)` and to obtain the equation we can do the square

`13^2=x^2+y^2` and the final equation is

`x^2+y^2-169=0`.