## Intermediate Algebra for College Students (7th Edition)

Use standard form of equation of circles; $(x-a)^2+(y-b)^2=r^2$ Here, $r$ defines radius and $(a,b)$ defines center. In the given equation $x^2+y^2-4=0$, it can be seen that the coefficients of $x^2$ and $y^2$ are having same sign . Thus, the graph of the given equation corresponds to a circle.