Mathematics
The following figure shows a circle with centre O and diameter PQ. Point R lies on the circumference of the circle such that PR = QR and PR = 4 cm.

Calculate the radius of the given circle and state its value correct to two decimal places.
Related Questions
In a circle with centre O and diameter AB; angle APB is the angle of semicircle. If PA = PB; find the measure of each angle of triangle APB.
In the following figure, O is the centre of the circle and AB is a diameter.

C and D are the points on the circumference of the circle such that ∠CAB = 35° and ∠ABD = 55°. Find the measures of angles CAD and CBD.
In the following figure, PQ and PR are the tangent to the circle with centre O. Line segment AC touch the circle at point B.

(i) State the relation between tangent PQ and PR.
Also show that:
(ii) PQ = PA + AB
(iii) PR = PC + CB
(iv) PQ + PR = Perimeter of ΔPAC.
From an external point P, the tangent PA is drawn to the circle with centre O.
(i) If OP = 20 cm and tangent PA = 16 cm find the diameter of the circle.
(ii) If diameter of the circle is 20 cm and tangent PA = 24 cm, find the length of OP.