Jul 5, 2016

If circle, eqn. $: {x}^{2} + {y}^{2} = 15.$

#### Explanation:

Area of circle $= \pi {r}^{2} = 15 \pi \Rightarrow {r}^{2} = 15$.

If an Ellipse, I am not sure that we can find its eqn.

Area of Ellipse $= \pi a b = 15 \pi \Rightarrow a b = 15.$

To find $a \mathmr{and} b$ individually, one more cond. is required.

I hope this will be helpful! Enjoy!