# What is the polar equation for x^2+y^2=9?

Apr 7, 2018

$x = 3 \cos \theta$
$y = 3 \sin \theta$

#### Explanation:

the equation ${y}^{2} + {x}^{2} = 9$ is an equation of a circle

it's radius is $3$ and it's center is $\left(0 , 0\right)$

and to find the the polar equation of a circle you use the following formula
$x = h + r \cos \theta$
$y = k + r \sin \theta$

where $\left(h , k\right)$ is the center of the circle which is in this case is $\left(0 , 0\right)$
and by substituting You get:
$x = 3 \cos \theta$
$y = 3 \sin \theta$