**1.** A circle may be regarded as a collection of points in a plane at a fixed distance from a fixed point. The fixed point is called the centre of the circle. The fixed distance between the centre of the circle and the circumference, is called radius.

**2.** The perimeter of the circle is referred to as the circumference of the circle.

**3.** A chord of a circle is a line segment joining any two points on the circumference.

**4.** An arc of a circle is a part of the circumference.

**5.** A diameter of a circle is a chord which passes through the centre of the circle.

**6.** A line, which intersects the circle in two distinct points, is called a secant.

**7.** A line which has only one point common to the circle is called a tangent to the circle.

**8.** There is one and only one tangent at a point of the circle.

**9.** The tangent at any point of a circle is perpendicular to the radius through the point of contact.

**10.** No tangent can be drawn from a point inside the circle.

**11.** The lengths of tangents drawn from an external point to a circle are equal.

**12.** The perpendicular at the point of contact to the tangent to a circle passes through the centre of the circle.

**13.** Tangents drawn at the end points of a diameter of a circle are parallel.

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