1不是 2cm:3cm≠4cm:1cm
2不是1.5cm:2.5cm≠4.5cm:6.5cm
3不是 1.1cm:2.2cm≠3.3cm:4.4cm
4是 1cm:2cm=2cm:4cm
找内向积等于外向积,即a:b=c:d可写为ad=bc