(123456789/123456788-123456788/123456789)除以(1/123456788+1/123456789)
=(1+1/123456788-(1-1/123456789))除以(1/123456788+1/123456789)
=(1+1/123456788-1+1/123456789))除以(1/123456788+1/123456789)
=(1/123456788+1/123456789))除以(1/123456788+1/123456789)
=1