（-1/42）÷（-1/6-3/14+2/3-4/7）=-1÷（-1/6x42-3/14x42+2/3x42-4/7x42）=-1÷（-7-9+28-24）=-1÷（-12）=1/12
（-1/42）÷（-1/6）-3/14+2/3-4/7=1/7-3/14+2/3-4/7=(1/7-3/14-4/7)+2/3=-9/14+2/3=1/42
