0.666666.= 0.6 + 0.06 + 0.006 + 0.0006 + .= 0.6 + 0.6/10 + 0.006/100 + 0.0006/1000 + .= lim {0.6×[1 - (1/10)^n]/[1 - 1/10]} [这是等比数列：公比1/10,首项是0.6]n→∞= lim {0.6×[1 - (1/10)^n]/[9/10]} n...