屋顶变尖,角的总和会变吗?A sharper roof. A different angle sum?
折一个纸帐篷:屋顶越尖,三个内角的和会不会变小?Fold a paper tent. If the roof becomes sharper, does the sum of its three angles change?
欧几里得在《几何原本》I.32中,把三个角的问题转成了一条直线的问题。我们沿着这个办法试一试。In Elements I.32, Euclid turned a question about three angles into a question about a straight line. Let’s follow that idea.
依据:《几何原本》I.32Source: Euclid, Elements I.32





