# Thread: Find the center and radius of a circle (x-h)^2+(y-k)^2=r^2 (completion of square)

1. ## Find the center and radius of a circle (x-h)^2+(y-k)^2=r^2 (completion of square)

Is this bad? A program indicates that I'm correct for 2/3. What's my mistake?

I need to find (h,k) and the radius.

5x^2 -3x +5y^2 -9y -8 =0

x^2 -3x/5 +y^2 -9y/5 -8/5 =0

x^2 -3x/5 +(3/10)^2 -(3/10)^2 +y^2 -9y/5 +(9/10)^2 -(9/10)^2 -8/5 =0

(x -3/10)^2 -(3/10)^2 +(y -9/10)^2 -(9/10)^2 -8/5 =0

(x -3/10)^2 + (y -9/10)^2 -(3/10)^2 -(9/10)^2 -160/100 =0

(x -3/10)^2 +(y -9/10)^2 -9/100 -81/100 -160/100 =0

(x -3/10)^2 +(y -9/10)^2 = (250/100)^(1/2)

h: 3/10
k: 9/10
r: (5/2)^(1/2)

2. ## Re: Find the center and radius of a circle (x-h)^2+(y-k)^2=r^2 (completion of square)

Hello, SillyMath!

I see nothing wrong with your work.
Perhaps the program didn't like your radius?

. . $\displaystyle r \:=\:\sqrt{\frac{5}{2}} \:=\:\frac{\sqrt{10}}{2}$

3. ## Re: Find the center and radius of a circle (x-h)^2+(y-k)^2=r^2 (completion of square)

Thank you but it still won't take it.