0.998^6=(1-0.002)^6=[(1-0.002)^2]^3
(1-0.002)^2=1-0.004+0.002^2
因为是精确到0.001.所以0.002^2可以忽略不计
(1-0.004)^3=1-3×1×0.004-3×1×0.004^2+0.004^3≈1-0.012=0.988
0.998^6=(1-0.002)^6=[(1-0.002)^2]^3
(1-0.002)^2=1-0.004+0.002^2
因为是精确到0.001.所以0.002^2可以忽略不计
(1-0.004)^3=1-3×1×0.004-3×1×0.004^2+0.004^3≈1-0.012=0.988