A=[(1-22)/22][(1-32)/32]...[(1-20152)/20152]
A=[(1+2)(1-2)/22][(1-3)(1+3)/32]...[(1-2015)(1+2015)/20152]
=[(-1).3/2.2][(-2).4/3.3]...[-2014.2016/2015.2015]
=[(-1)(-2)(-3)...(-2013)(-2014).3.4.5...2015]/(2.2.3.3.4.4....2015.2015)
=[2(-3)...(-2014)]/(2.2.3.4.5....2015)
=(-3)(-4)...(-2014)/2.3.4.5....2015
=[-(3.4.5.6....2014)]/(2.3.4...2015)
=-1/1.2015=-1/2015