`x^2 + y^2 + 2x - 2y - 4 = 0` Find the radius.
The general equation with a circle with center (h, k) and radius, r, is:
`(x - h)^2 + (y - k)^2 = r^2`
` `We need to complete the square in order to write the original equation in general equation form.
First: `(x^2 + 2x + a) + (y^2 - 2y + b) = 4`
In order to find a and b divide middle term of each trinomial by 2 then square it. This gives us:
`(x^2 + 2x + 1) + (y^2 - 2y + 1) = 4 + 1 + 1`
`(x + 1)^2 + (y - 1)^2 = 6`
Since `6 = r^2,`
Therefore, the radius of the circle is `sqrt(6).`