Perhaps you should try some spelling variations:
thieu xanh » chieu xanh, thien anh, thien danh
hieu manh » chieu xanh, hieu nganh, dieu hanh
hang hang » nang hang, cang thang, hung thang
hang cong » dang cong, hang nong, thanh cong
bang cong » dang cong, bang song, dung cong
bai toan » bai tap
toan cao » toan ban, toan tap
hang ca » hang va, nang cao, hang tai

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc ((thieu xanh) or (hieu manh)) - hang hang ca ((hang cong) OR (bang cong)) bai toan cao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc ((thieu xanh) OR (hieu manh)) - hang hang ca ((hang cong) OR (bang cong)) bai toan cao.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc ((thieu xanh) or (hieu manh)) - hang hang ca ((hang cong) OR (bang cong)) bai toan cao".
• Adding a wildcard symbol may retrieve word variants: hoc ((thieu xanh) or (hieu manh)) - hang hang ca ((hang cong) OR (bang cong)) bai toan cao*.