How many points lie on the graph of $x^2+y^2=0$x2+y2=0?

How many points lie on the graph of $x^2+y^2=-81$x2+y2=−81?

State the equation of the circle.

A circle has its centre at the origin and a radius of $4$4 units.

Apply the geometry of conic sections

Apply the geometry of conic sections in solving problems