(1/8+1/24+1/48+1/80+1/120+1/168)*56
=(2/8+2/24+2/48+2/80+2/120+2/168)*28
=[2/2*4+2/4*6+2/6*8+2/8*10+2/10*12+2/12*14)*28
=[(1/2-1/4)+(1/4-1/6)+(1/6-1/8)+(1/8-1/10)+(1/10-1/12)+(1/12-1/14)]*28
=(1/2-1/14)*28
=1/2*28-1/14*28
=14-2
=12
(1/8+1/24+1/48+1/80+1/120+1/168)*56
=(2/8+2/24+2/48+2/80+2/120+2/168)*28
=[2/2*4+2/4*6+2/6*8+2/8*10+2/10*12+2/12*14)*28
=[(1/2-1/4)+(1/4-1/6)+(1/6-1/8)+(1/8-1/10)+(1/10-1/12)+(1/12-1/14)]*28
=(1/2-1/14)*28
=1/2*28-1/14*28
=14-2
=12