CIRCLES A circle is a simple shape in Euclidean geometry. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant. shapeEuclidean geometrypointsplanecentre SECANT- A line which intersects a circle in two distinct points in called a secant. TANGENT – A Line meeting a circle only in one point is called a tangent to the circle at that point. Tangent Secant

NUMBER OF TANGENTS TO A CIRCLE (i)There is no tangent passing through a point lying inside the circle (ii)There is one and only one tangent passing through a point lying on a circle. (iii) There are exactly two tangents through a point lying outside a circle. LENGTH OF TANGENT The length of the line segment of the tangent between a given point and the given point of contact with the circle is called the length of the tangent from the point to the circle.

RESULTS ON TANGENTS THEOREM 1 The tangent at any point of a circle is perpendicular to the radius through the point of contact.. O A B R Q P GIVEN A Circle with centre O and a tangent AB at a point P of the circle. TO PROVE OP AB. CONTRCUTION Take a point Q, other than P, on AB. Join OQ. PROOF:- Q is a Point on the tangent AB, other than the point of contact P. Hence- Q Lies outside the circle. Let OQ intersect the circle at R. Then, OR < OQ [ a part is less than the whole.] (i) But, OP= OR [ radii of the same circle.] (ii) Hence- OP< OQ [ from (i) and (ii)

Thus, OP shorter than any other line segment joining O to any points of AB, other than P. But, the shortest distance between a point and a line is the perpendicular distance. OP AB Proved

THEOREM 2 (Converse of Theorem 1) A Line drawn through the end of a radius and perpendicular to it is tangent to the circle. A B. 0 PQ GIVEN A Circle with centre O in which OP is radius and AB is a line through P such that OP AB. TO PROVE AB is tangent to the circle at the point P. CONSTRUCTION Take a point Q, different from P, on AB. Join OQ. PROOF We Know that the perpendicular distance from a point to a line is the shortest distance between them. OP AB= OP is the shortest distance from O to AB. OP< OQ Q Lies outside the circle AB meets the circle at the point at P only Hence AB is the tangent to the circle at the point P..

END PRESENTED BY:- UJJWAL HARSH