因为s1=V0t+at^2/2
s2=V0*2t+a*(2t)^2/2-V0t-at^2/2
=V0t+3at^2/2
s3=3V0t+9at^2/2-2V0t-4at^2/2=V0t+5at^2/2
...
sn-1=(n-1)V0t+(n-1)^2*at^2/2-(n-2)V0t-(n-2)^2*at^2/2
=V0t+(2n-3)at^2/2
sn=nV0t+n^2*at^2/2-(n-1)V0t-(n-1)^2*at^2/2
=V0t+(2n-1)at^2/2
所以s2-s1=s3－s2=sn－sn－1=at2