(a^2014-1)/a^2015
= a^2014/a^2015 - (1/a^2015)
= 1/a - 1/a^2015
a=2时,原式 = 1/2 - 1/2^2015 ≈ 1/2a=-3/4呢？a=-3/4时：
= 1/(-3/4) - 1/(-3/4)^2015

≈ -4/3