M=1/2+1/2.7+1/7.5+1/5.13+1/13.8+1/8.19
M=1/2-1/2+1/7-1/7+1/5-1/5+1/13-1/13+1/8-1/8+1/19
M=1/2-1/19
M=17/38
M=1/2(1/2+1/14+1/35+1/65+1/104+1/152)
M=1/4+1/28+1/70+1/130+1/208+1/304
M=1/1.4+1/4.7+1/7.10+1/10.13+1/13.16+1/16.19
M=1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16+1/16-1/19
M=1-1/19
M=18/19
Vậy M=18/19
cách 1\(M=1/2(1/2+1/14+1/35+1/65+1/104+1/152) M=1/4+1/28+1/70+1/130+1/208+1/304 M=1/1.4+1/4.7+1/7.10+1/10.13+1/13.16+1/16.19 M=1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16+1/16-1/19 M=1-1/19 M=18/19 Vậy M=18/19\)
cách 2 M=1/2(1/2+1/14+1/35+1/65+1/104+1/152) M=1/4+1/28+1/70+1/130+1/208+1/304 M=1/1.4+1/4.7+1/7.10+1/10.13+1/13.16+1/16.19 M=1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16+1/16-1/19 M=1-1/19 M=18/19 Vậy M=18/19
M=1/2+1/2.7+1/7.5+1/5.13+1/13.8+1/8.9
M=1/2-1/2+1/7-1/7+1/5-1/5+1/13-1/13+1/8-1/8+1/19
M=1/2-1/19=17/38