[latex]it a_{2016} = 2a_{1016} (1) \;\ a_{2016} = a_{16} +2000r (2) \;\ a_{1016} =a_{16} +1000r (3) [/latex] [latex]it (1), (2), (3) Rightarrow a_{16} +2000r = 2(a_{16} +1000r) Rightarrow \;\ Rightarrow a_{16} +2000r = 2a_{16} +2000r Rightarrow 2000r-2000r=2a_{16}-a_{16} Rightarrow \;\ Rightarrow 0=a_{16} Rightarrow a_{16} = 0[/latex]