2a
(-3/2)a^2
(4/3)a^3
(-5/4)a^4
(6/5)a^5
(-7/6)a^6
.
an=(-1)^(n+1)*(n+1)/n*a^n
a2008=(-1)^(2008+1)*(2008+1)/2008*a^2008=(-2009/2008)a^2008
2a
(-3/2)a^2
(4/3)a^3
(-5/4)a^4
(6/5)a^5
(-7/6)a^6
.
an=(-1)^(n+1)*(n+1)/n*a^n
a2008=(-1)^(2008+1)*(2008+1)/2008*a^2008=(-2009/2008)a^2008