即丨ab-2丨+丨b-1丨=0
则ab-2=b-1=0
所以b=1
a=2
所以原式=1/1×2+1/2×3+……+1/2015×2016
=1-1/2+1/2-1/3+……+1/2015-1/206
=1-1/2016
=2015/2016