# Chapter 9 Quadratic Relations and Conic Sections - 9.3 Graph and Write Equations of Circles - 9.3 Exercises - Skill Practice - Page 629: 24

$$x^2+y^2=4$$

#### Work Step by Step

We know that the equation for a circle centered at the origin of radius r is $x^2+y^2=r^2$. Thus, the equation for this circle is: $$x^2+y^2=2^2 \\ x^2+y^2=4$$

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