Perhaps you should try some spelling variations:
thieu xanh » chieu xanh, hieu manh, thien anh
cang thang » dang thanh
cong thanh » dong thanh, cong trinh, cong tan
hoc thieu » toc thieu, hoc hien
tap toan » tap doan, tap quan
bai toan » bai tap
va dung » van dung, va duong, vat dung

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: hoc thieu xanh - ((cang thang) OR (cong thanh)) va dung trong ((tap toan) OR (bai toan)) ban~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc thieu xanh - ((cang thang) or (cong thanh)) va dung trong ((tap toan) OR (bai toan)) ban~".
• Adding a wildcard symbol may retrieve word variants: hoc thieu xanh - ((cang thang) or (cong thanh)) va dung trong ((tap toan) OR (bai toan)) ban*.