0.1+0.12+0.123+0.1234+.+0.123456789 （有9个0.1,8个0.02,7个0.003...)=0.1*9+0.02*8+0.003*7+0.0004*6……+0.000000009*1=0.9+0.16+0.021+0.0024+0.00025+0.000024+0.0000021+0.00000016+0.000000009=1.083676269...