Perhaps you should try some spelling variations:
differences equations » difference equations, differential equations, differentes situations
difference equation » difference equations, differential equation, differential equations
facial differences » racial differences, social differences, fatal differences
facial difference » racial difference, racial differences, social difference

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (( facial differences equations ) OR ( facial difference equation )).
• Adding a wildcard symbol may retrieve word variants: (( facial differences equations ) or ( facial difference equation ))*.