A circle has infinitely many tangents, touching the circle at infinite points on its circumference.
A tangent touches the circle only on its boundary and do not cross through it.
A circle can have two parallel tangents at the most.
If the angle between two radii of a circle is 110º, then the angle between tangents is 180º − 110º = 70º. (By circles and tangents properties)
Since the tangent is perpendicular to the radius of the circle, then the angle between them is 90º.
Thus, OA is the hypotenuse for the right triangle OAB, which is right-angled at B. As we know, for any right triangle, the hypotenuse is the longest side.
Therefore the length of the tangent from an external point is always less than the OA.
If a parallelogram circumscribes a circle, then it is a Rhombus.
We know that the sum of the angle between two radii of a circle and the angle between the tangents at the ends of the radii is 180°.
Therefore, the angle between the tangents at the ends of the radii = 180° – 130° = 50°
A line intersecting a circle in two points is called a Secant.
The tangent to a circle is perpendicular to the radius through the point of contact.
Given,
Distance between two parallel tangents = 18 cm
That means, diameter = 18 cm
Therefore, radius of the circle = $\dfrac{18}{2}$ = 9 cm