Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, hang cong
hieu lang » chieu sang, hieu quang, nhieu tang
thang va » hang va, trang va, thong va
tac toan » tap toan, hach toan, tich toan
tam toan » tap toan, tam than, pham toan
ho hieu » ho chieu, hoi hieu, nho hieu
tang va » trang va, tang van, tang vat

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 - anh ((tang va) OR (thang va)) nhung cong ((tac toan) OR (tam toan)) cau~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "ho hieu lang - anh ((tang va) or (thang va)) nhung cong ((tac toan) OR (tam toan)) cau~".
• Adding a wildcard symbol may retrieve word variants: ho hieu lang - anh ((tang va) or (thang va)) nhung cong ((tac toan) OR (tam toan)) cau*.