二分之一减三分之一加四分之一减五分之一加六分之一减七分之一
=1/2x3+1/4x5+1/6x7
=1/6+1/20+1/42
=7/42+1/42+1/20
=8/42+1/20
=4/21+1/20
=80/420+21/420
=101/420
解：1/2-1/3+1/4-1/5+1/6-1/7
=（1/2-1/3）+（1/4-1/5）+1/6-1/7
=1/6+1/20+1/6-1/7
=1/3+1/20-1/7
=（140+21-60）/420
=101/420
1/2-1/3+1/4-1/5+1/6-1/7
=(1/2+1/4)+(1/6-1/3)-1/7
=3/4-1/6-1/7
=63/84-14/84-12/84
=37/84
内容全部来源于网络收集，如有侵权，请联系网站删除：QQ：24596024