so my equation is x^{2}+y^{2}-4x+2y-4=0

i know the formula is (x-h)^{2}+(y-k)^{2}=r^{2}

x^{2}-4x+y^{2}+2y-4=0

the Y is (y-2)^{2}which makes my k equal to positive 2 just having trouble with the h and radius

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- Oct 20th 2012, 08:38 AMM670Need help finding (h,K,) and the radius of a circle
so my equation is x

^{2}+y^{2}-4x+2y-4=0

i know the formula is (x-h)^{2}+(y-k)^{2}=r^{2}

x^{2}-4x+y^{2}+2y-4=0

the Y is (y-2)^{2}which makes my k equal to positive 2 just having trouble with the h and radius - Oct 20th 2012, 08:50 AMskeeterRe: Need help finding (h,K,) and the radius of a circle
$\displaystyle x^2+y^2-4x+2y-4 = 0$

$\displaystyle x^2 - 4x + y^2 + 2y = 4$

complete the square for x and y ...

$\displaystyle (x^2 - 4x + 4) + (y^2 + 2y + 1) = 4 + 4 + 1$

finish it ... - Oct 20th 2012, 09:03 AMSorobanRe: Need help finding (h,K,) and the radius of a circle
Hello, M670!

Sorry, your algebra is off . . .

Quote:

$\displaystyle \text{Find the center and radius of the circle: }\:x^2+y^2-4x+2y-4\:=\:0$

We must "complete the square".

$\displaystyle \begin{array}{c}x^2 + y^2 - 4x + 2y - 4 \:=\:0 \\ \\ x^2 - 4x + y^2 + 2y \:=\:4 \\ \\ x^2 - 4x \,{\color{red}+\, 4} + y^2 + 2y {\color{blue}\,+\, 1} \:=\:4{\color{red}\,+\,4}{\color{blue}\,+\,1} \\ \\ (x-2)^2 +(y+1)^2 \:=\:9 \end{array}$

The circle has center $\displaystyle (2,\text{-}1)$ and radius $\displaystyle r = 3.$

- Oct 20th 2012, 09:33 AMM670Re: Need help finding (h,K,) and the radius of a circle
ok I understand that question but given this example here 5 x^2 - 10 x +5 y^2 - 8 y - 6 = 0 .

I worked it down to (x-1)^2 and (y-0.8)^2 =

I divided out 5 and was left with x^2-2x+y^2-1.6y-1.2=0

then its x^2-2x+1 + y^2-1.6y ?= 1.2-1 (?) - Oct 20th 2012, 10:01 AMPlatoRe: Need help finding (h,K,) and the radius of a circle
- Oct 20th 2012, 10:13 AMM670Re: Need help finding (h,K,) and the radius of a circle
- Oct 20th 2012, 10:15 AMM670Re: Need help finding (h,K,) and the radius of a circle
How do you figure it out when you have a fraction or decimal to complete the squares?

- Oct 20th 2012, 10:23 AMPlatoRe: Need help finding (h,K,) and the radius of a circle