Q&A From am external point P，tangents PA and PB are drawn to a circle. From a point Q on the major (or minor) arc AB， perpendiculars are drawn to AB， PA，and PB. Prove that the perpendicular to AB is the mean proportional between the other two perpendiculars.

Q&A In the \triangle ABC，in which AB = 12，BC = 18，and AC = 25，a semicircle is drawn so that its diameter lies on AC, and so that it is tangent to AB and BC. If O is the center of the circle,

Q&A Determine the angle (in radians) subtended at the centre of a circle of radius 3 cm by each of the following arcs:

Q&A Tell whether the line or segment is best described as a chord, a secant, a tangent, a diameter, or a radius of the circle.