Explore the formula for the area of a circle, by cutting it into sectors and rearranging the sectors to form a figure close to a parallelogram. By increasing the no. of sectors, students observe that the figure tends to a rectangle and get the formula for the area of the circle by finding the area of this rectangle.
See also how I design the applets in http://www.geogebratube.org/material/show/id/15215.
Anthony Or. GeoGebra Institute of Hong Kong.
orchiming@gmail.com
（繁體中文版：http://www.geogebratube.org/material/show/id/550）
