设20m时影长为X.
X/(X+20)=1.6/8
8X=1.6X+32
6.4X=32
X=5m
设14m时影长为Y.
Y/(Y+14)=1.6/8
8Y=1.6Y+22.4
6.4Y=22.4
Y=3.5m
小明的影长由5m变成3.5m.