Point A and point B show where a cyclone enter and leave the 800km circle that centred at Hong Kong (point O). The distance between A and B is 1200km. What is the shortest distance of the cyclone from Hong Kong?[br][br]This will initiate some discussion about the meaning of shortest distance and how to identify it, leading to analysis of a chord. You may move A and B to create another chord of the same length and discuss what will be the same.[br][br]Drag the slider d to see how the cyclone C is moving. On the left, [math]p[/math] represents the length of AB in km.[br]