*Circle The locus of a point P (x, y) which moves in a plane so that its distance from a fixed point is always a constant. The fixed point is called the centre C (u, v) of the circle and the constant distance is called its radius (R).
Also a radius of a circle is a straight line joining the centre any point on the circumference. As CP = R, thus using displacement formula we can write
The above expression is called Central form of a circle.
A circle can also be expressed as
ax2 + by2 + 2 gx + 2 fy + c = 0
This expression is called general form of a circle.
Here (-g, -f) is the center of the circle
If centre of a circle coincides with origin O (0, 0) then the above expression can be written as,
x2 + y2 = R2.
This expression is called Standard form of a circle.