[justify][/justify][justify]You can spice up your presentations using the [b][url=https://appsource.microsoft.com/en-us/product/office/wa104363477]GeoGebra for PowerPoint[/url][/b].  You can pick an existing construction or start from scratch: all your changes will be saved in the presentation.[/justify]

[center][size=200][url]http://ggbtu.be/microsoft[/url][/size][/center]

[b]Click the "▶" button. Observe the angles turned by the car at the corners.[br]Drag the green points. Check the "Show Measurement" box to see the measurements of the angles.[br][/b]中文版：[url=https://ggbm.at/551]https://ggbm.at/551[/url]

[b]1. What is a + b + c + d + e, the total angles turned by the car?[br]2. a, b, c, d, e are called the exterior angles of the convex pentagon.[br]　　In general, what is the sum of all exterior angles of a convex polygon?[br]3. How would you modify the result if the pentagon is NOT convex?[br][/b][br]Anthony Or. GeoGebra Institute of Hong Kong.