①：由于当n=1时,a1 = -1；n=2时,a2 = 2；n=3时,a3 = -3……；当n=n时,an = n(-1)^n即：数列an的通项公式为：an = n(-1)^n②：由于当n=1时,a1 = 1/2；n=2时,a2 = -4/5；n=3时,a3 = 9/10……；当n=n时,an = [(-1)^n]*...