解：原式=1/42÷[1/2-1/3+5/7+4/9*(-6)]=1/42÷[3/6-2/6+5/7-8/3]=1/42÷[1/6+5/7-16/6]=1/42÷[7/42+30/42-112/42]=1/42÷(37-112)/42=1/42×42/(-75)=-1/75
