Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
manh tuong » manh tung, manh cuong, minh tuong
nhung cong » dung cong, thong cong, hang cong
hoc hieu » hoc thieu, hoc hien, doc hieu
tuong va » truong va, thuong va, luong va
bai toan » bai tap
tam toan » tap toan, tam than, pham toan

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc hieu quang - manh tuong va nhung cong ((bai toan) or (tam toan)) cao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc hieu quang - manh tuong va nhung cong ((bai toan) OR (tam toan)) cao.
• Adding a wildcard symbol may retrieve word variants: hoc hieu quang - manh tuong va nhung cong ((bai toan) or (tam toan)) cao*.