a1=cosπ/2+1 a2=2cos2π/2+1a3=3cos3π/2+1a4=4cos4π/2+1...Sn = S{ncosnπ}/2 + nS{ncosnπ} = -1+2-3+4-5+6+...+n*(-1)^nS2012 = (2012/2 )/2+2012 = 2515
3016
