Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
quang dung » quang trung, ung dung, cuong dung
hieu sang » chieu sang, hieu lang, nhieu tang
trong van » trong cac
qua dung » su dung, qua song, qua cong
van toan » van tuan, van tan, van thanh
toan ban » van ban

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc ((hieu sang) or (hieu quang)) - tinh quang ((qua dung) OR (quang dung)) trong van toan ban~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc ((hieu sang) OR (hieu quang)) - tinh quang ((qua dung) OR (quang dung)) trong van toan ban.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc ((hieu sang) or (hieu quang)) - tinh quang ((qua dung) OR (quang dung)) trong van toan ban".
• Adding a wildcard symbol may retrieve word variants: doc ((hieu sang) or (hieu quang)) - tinh quang ((qua dung) OR (quang dung)) trong van toan ban*.