Circle with Centre (h,k) and Radius r (Leaving Cert Mathematics): Flashcards

$(x - h)^2 + (y - k)^2 = r^2$

Centre of the circle

Radius of the circle

Equidistant from centre

$r^2$ (radius squared)

Distance formula: centre to point

$(x - 2)^2 + (y + 3)^2$ (opposite signs)

$(x - 2)^2 + (y + 3)^2 = 25$

$(-3, 4)$ (opposite signs)

$sqrt{8} = 2sqrt{2}$

$sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$

Sign errors with centre coordinates