x^2 + y^2 + 6x=0. How would I go about finding the radius and center? What's the basic method?

-Thanks!

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- May 12th 2008, 12:55 PMHibijibiFinding Center And Radius of Circle
x^2 + y^2 + 6x=0. How would I go about finding the radius and center? What's the basic method?

-Thanks! - May 12th 2008, 01:13 PMMoo
Hello,

To complete the squares :D

I'll do it in a newly way to me... lol

$\displaystyle x^2+6x=x(x+6)=((x+3)-3)((x+3)+3)=(x+3)^2-3^2=(x+3)^2-9$

(I know you can do it in a shorter way... find it ! :D)

Hence the equation becomes :

$\displaystyle (x+3)^2+y^2-9=0 \Longleftrightarrow (x+3)^2+y^2=9$

We know that the equation of a circle, center $\displaystyle O(x_O,y_O)$ and radius R is :

$\displaystyle (x-x_O)^2+(y-y_O)^2=R^2$

Conclude (Sun)