# Chapter 9 Quadratic Relations and Conic Sections - 9.3 Graph and Write Equations of Circles - 9.3 Exercises - Skill Practice - Page 630: 36

$$x^2+y^2=85$$

#### Work Step by Step

Since the center is at the origin, we use the distance formula to find that the radius must be: $$\sqrt{\left(-9-0\right)^2+\left(2-0\right)^2} \\ \sqrt{85}$$ Thus, it follows: $$x^2+y^2=r^2$$ $$x^2+y^2=85$$

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