Perhaps you should try some spelling variations:
"rational differences equations" » "rational difference equation", "rational differential equations", "rational differentes situations", "rational difference equations", "regional differences equations", "operational differences equations"
"national differences equations" » "national difference equation", "national differential equations", "national differentes situations", "functional differences equations", "regional differences equations", "generational 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 ("national differences equations"))) OR ("racial difference equations")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"rational differences equations\") OR (\"national differences equations\"))) or (\"racial difference equations\"))".
• Removing quotes may allow a broader search: (((( rational differences equations ) OR ( national differences equations ))) or ( racial difference equations )).
• Adding a wildcard symbol may retrieve word variants: (((("rational differences equations") OR ("national differences equations"))) or ("racial difference equations"))*.