9.7. Extension: Writing and Graphing the Equations of Circles http://www.ck12.org
(− 1 − 4 )^2 +( 2 + 1 )^2 =r^2
(− 5 )^2 +( 3 )^2 =r^2
25 + 9 =r^2
34 =r^2At this point, we don’t need to solve forrbecauser^2 is what is in the equation. Substituting in 34 forr^2 , we have
(x− 4 )^2 +(y+ 1 )^2 =34.
Review Questions
Find the center and radius of each circle. Then, graph each circle.
1.(x+ 5 )^2 +(y− 3 )^2 = 16
2.x^2 +(y+ 8 )^2 = 4
3.(x− 7 )^2 +(y− 10 )^2 = 20
4.(x+ 2 )^2 +y^2 = 8Find the equation of the circles below.