## Precalculus (6th Edition) Blitzer

From the equation, we have $a=3, b=1, c=\sqrt {a^2+b^2}=\sqrt {10}\approx3.16$. The center of the hyperbola is at $(0,0)$ and the transverse axis is horizontal. Thus, the foci can be located at $(\pm\sqrt {10},0)$