Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
nhung cong » dung cong, thong cong, hang cong
hieu lang » chieu sang, nhieu tang, hieu van
cong bai » cuong bai, cong hai, cung bai
bai toan » bai tap
toan cao » toan ban, toan tap
mang va » mang vua, bang va, dang va

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: nho ((hieu lang) OR (hieu quang)) - hanh ((mang va) OR (hang va)) nhung cong bai toan cao~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "nho ((hieu lang) OR (hieu quang)) - hanh ((mang va) or (hang va)) nhung cong bai toan cao~".
• Adding a wildcard symbol may retrieve word variants: nho ((hieu lang) OR (hieu quang)) - hanh ((mang va) or (hang va)) nhung cong bai toan cao*.