### Home > INT3 > Chapter 3 > Lesson 3.1.1 > Problem3-18

3-18.

What are the center and radius of each circle? Rewrite the equations if necessary. Homework Help ✎

Rewrite each equation in graphing form.

$(x-h)^{2}+(y-k)^{2}= \ r^{2}$

1. $(y-7)^2=25-(x-3)^2$

center: $(3,7)$

radius: $5$

1. $x^2+y^2+10y=-9$

Completing the square for $y$ is necessary.

center: $(0,−5)$

radius: $4$

1. $x^2+y^2+18x-8y+47=0$

Complete the square for both $x$ and $y$.

center: $(−9,4)$

radius: $\sqrt{50}$

1. $y^2+(x-3)^2=1$

$(x−3)^2+(y−0)^2=1$