A circle is the locus of a point which moves in such a way that its distance from a fixed point is constant. The fixed point is called the centre of the circle and the constant distance is called the radius of the circle.
Tangents and Normal’s
Definition by Online Tutor:
A tangent to a curve at a point is defined as the limiting positions of a secant obtained by joining the given point to another point in vicinity on the curve as the scond point tends to the first point along the curve or as the limiting position of a secant obtained by joining two points on the curve in the vicinity of the given point as both the points tend to the given point.
Two tangents, real or imaginary, can be drawn to a circle from a point in the plane. The tangents are real and distinct if the point is outside the circle, real and coincident if the point is on the circle and imaginary if the point is inside the circle.
The normal to a curve at a point is defined and the straight line passing through the point and perpendicular to the tangent at the point. In case of a circle every normal passes through the centre of the circle.
Chord of Contact:
From a point P(x, y) two tangents PA and PB can be drawn to the circle. The chord AB joining the points of contact A and B of the tangents from P is called the chord of contact of P(x, y) with respect to the circle.