Circle is a probably the easiest of all the conic sections, and also helps in other conic sections.

Past year trend

As we can see from the graph, there is not even a single year when questions are not asked from circles both in JEE-Advanced and JEE-Mains.

Topics

Circles is one of the basic conic which is a special case of ellipse. The general equation of a circle with radius r and centre as (a,b) is given by (x-a)^2+(y-b)^2=r^2.

For a circle (x)^2+(y)^2=a^2:

The equation of tangent is given by xcostheta+ysintheta=a.

The chord of contact from a point (p,q) is px+qy=a^2.

The equation of a director circle is x^2+y^2=2a^2.

For two circles S_1 and S_2, family of circles is given by S_1+lambdaS_2=0 and radical axis is given by S_1-S_2=0.