- The assertion (A) is true: Tangents drawn from an external point to a circle are equal in length, and the angle between the tangent and the radius at the point of contact is \(90^\circ\). The quadrilateral formed by the tangents and the radii of the circle from point \(P\) is cyclic because the sum of opposite angles equals \(180^\circ\), a property of cyclic quadrilaterals.
- The reason (R) is true: In a cyclic quadrilateral, opposite angles are supplementary, meaning the sum of opposite angles is always \(180^\circ\).
Since both the assertion and reason are true, and the reason explains the assertion, the correct answer is (a).