(01)一張長方形的白紙,看圖就明白了,
(02)對摺,看圖就明白了,
(03)對摺,看圖就明白了,
(04)再對摺,如圖,看圖就明白了,
(05)如圖,看圖就明白了,
(06)如圖,看圖就明白了,
(07)如圖,看圖就明白了,
(08)如圖,看圖就明白了,
(09)如圖,看圖就明白 了,
(10)如圖,看圖就明白了,
(11)如圖,看圖就明白了,