圓上的角與弧長的關係

Arc Length and Angles in Circles

以固定大小的角畫圖

Tracing with Constant Angle

延申正弦公式的無言證明

Extended Sine Formula

摺摺摺，摺出三角另一心

Fold the segments into the circle, what do you observe?

將這些弓形向圓內摺，你觀察到了什麼？

4 Centers of Triangle by Folding a Circle

一些外心與垂心之間的有趣關係

Some Interesting Relations Between Circumcenter and Orthocenter

不在圓周上的角

Angles NOT lying on Circumference

交錯弓形圓周角的另一種理解

Alternative Understanding of Angle in Alternate Segment

直線與平面垂直嗎？

Do we have enough evidence? How much is enough?

我們有足夠的證據嗎？多少才算足夠？

Is the Line Perpendicular to the Plane?

互相垂直的三腳架頂點投影

What are the special condition(s) in the tetrahedron so that the projection of vertex lies on the 4 special centres of base?

四面體滿足什麼特殊條件，才能使頂點的投影落在底三角形的四心？

Projection onto 4 Centers of Triangles

互相垂直的三腳架頂點投影

What is the relationship between the projection of vertex and base triangle?

若三腳互相垂直，探索四面體頂點投影與其底三角形之間的什麼關係

Projection of Perpendicular Tripod

這是正方形嗎？

I and J are the mid-points of the sides of a cube, is the cross-section a square?

I 和 J 是立方體邊上的中點，那麼該立方體的橫截面是正方形嗎？

Cross Section of a Cube