1/2+(2/3+1/3)+(3/4+2/4+1/4)+……+(39/40+38/40+……2/40+1/40)
=0.5+1+1.5+2+...+20
=(0.5+20)+(1+19.5)+...+(10+10.5)
=20*20.5
=20*(20+0.5)
=400+10
=410(1-1/2+1/3+1/6)X(1-1/4+1/5+1/20)X(1-1/6+1/7+1/42)(1-1/2+1/3+1/6)X(1-1/4+1/5+1/20)X(1-1/6+1/7+1/42)=(1+(-1/2+1/3)+1/6)X(1+(-1/4+1/5)+1/20)X(1+(-1/6+1/7)+1/42)=(1-1/6+1/6)X(1-1/20+1/20)X(1-1/42+1/42)=1X1X1=1第一个=号后面的（1+（-1/2+1/3)是什么意思，是+还是-啊把这二项合并起来算啊！帅歌！1.25X88.6/15X8+8X1/3X1.1/4-125%X78.2/3X8+2/5X3.1/3