Question

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

Answer 1

`x=3costheta`
`y=3sintheta`

Explanation:

the equation `y^2+x^2=9` is an equation of a circle

it's radius is `3` and it's center is `(0,0)`

and to find the the polar equation of a circle you use the following formula
`x=h+rcostheta`
`y=k+rsintheta`

where `(h,k)` is the center of the circle which is in this case is `(0,0)`
and by substituting You get:
`x=3costheta`
`y=3sintheta`