3/4-2/7+（-1/6）-（-2/3）-1
=3/4-2/7-1/6+2/3-1
=3/4-2/7-1/6+4/6-1
=3/4-2/7+1/2-1
=(3/4+1/2-1)-2/7
=1/4-2/7
=7/28-8/28
=-1/28