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# Find the equation of the circle with centre (0,2) and radius 2

$\begin {array} {1 1} (A)\;x^2-y^2-4y=0 & \quad (B)\;x^2+y^2-4y=0 \\ (C)\;x^2-y^2+4y=0 & \quad (D)\;x^2+y^2+4y=0 \end {array}$

Toolbox:
• Equation of a circle with centre (h, k) and radius r is given as $(x-h)^2+(y-k)^2=r^2$
Given coordinates of the centre is (0,2) and radius is 2.
Hence the equation of the circle is
$(x-0)^2+(y-2)^2=2^2$
On expanding we get,
$x^2+y^2-4y+4=4$
(i.e) $x^2+y^2-4y=0$ is the required equation of the circle.