Perhaps you should try some spelling variations:
hanh trinh » canh tranh, hanh chinh
hieu lang » chieu sang, hieu quang, nhieu tang
dung cong » dung trong
trinh va » trinh van, trinh vat, trinh ve
tap quan » tac quan
hai quan » tac quan
bai toan » bai tap
ho hieu » ho chieu, hoi hieu, nho hieu
va dung » van dung, va duong, vat dung

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: ho hieu lang - hanh trinh va dung cong ((((tap quan) OR (hai quan))) OR (bai toan)) cau~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "ho hieu lang - hanh trinh va dung cong ((((tap quan) OR (hai quan))) or (bai toan)) cau~".
• Adding a wildcard symbol may retrieve word variants: ho hieu lang - hanh trinh va dung cong ((((tap quan) OR (hai quan))) or (bai toan)) cau*.