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

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: (("rational differences equations") OR ("racial difference equations")).
• Removing quotes may allow a broader search: (( rational differences equations ) or ( racial difference equations )).
• Adding a wildcard symbol may retrieve word variants: (("rational differences equations") or ("racial difference equations"))*.