trapezoid

It just equal to few trapezoid area.

发现它相当于一些梯形面积之和。

I could have just drawn a trapezoid directly on my fabric, but I made a paper pattern to better illustrate how to draft the correct shape.

我可能只是一个梯形直接绘制在我的布，但我做了一纸模式，以更好地说明如何起草正确的形状。