Tính hợp lí: A= 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56
Giải thích
a)A=12.3+23.4+14.5+15.6+16.7+17.8
12−13+13−14+14−15+15−16+16−17+17−18=38
b)B=31.4+34.7+37.10+310.13+313.16+316.19
=1−14+14−17+17−110+110−113+113−116+116−119=1819
c)C=1331.4+34.7+37.10+310.13+313.16+316.19
=131−14+14−17+17−110+110−113+113−116+116−119=619
d)D=24+228+270+2130+2208+2304
=2331.4+34.7+37.10+310.13+313.16+316.19=1219