1. \(AD\) is the diameter of a circle and \(AB\) is a chord. If the diameter \(AD=34 cm\) and the chord \(AB=30 cm\), find the perpendicular distance from the centre of the circle to the chord \(AB\).
2. In the figure, if \(OA = 5 cm\), \(AB = 8 cm\) and \(OD\) is perpendicular to \(AB\), then \(CD\) is equal to:
