Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, hang cong
trung cua » truong cua, trung tuan, trung cap
bien cac » vien cac, dien cac, bien ca
hieu cua » hieu qua, dieu cua, bieu cua
tung cua » tuong cua, dung cua, tang cua
cong bai » cuong bai, cong hai, cung bai
bai toan » bai tap
toan cao » toan ban, toan tap

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

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