Posted by Shane on Sunday, September 1, 2013 at 2:01am.
A circle x^2 + y^ + 2x  2y 1 = 0 expressed in the following form (xh)^2 + (yk)^2 = r^2 where h, k are the coordinates of the centre. How is r the radius given?

maths  Graham, Sunday, September 1, 2013 at 2:15am
Rearrange into incomplete quadratics:
(x² + 2x) + (y²  2y) = 1
Complete the squares:
(x² + 2x + 1) + (y²  2y + 1) = 1 + 1 + 1
Express in the required form:
(x + 1)² + (y  1)² = (√3)²
Thus: h = 1, k = 1, r = √3
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