Perhaps you should try some spelling variations:
tieu xanh » tieu danh, chieu xanh, dieu hanh
hanh tang » hanh trang, anh tang, hanh mang
dung cong » dung trong
hang cong » dang cong, hang nong, bang cong
tap toan » tap doan, tap quan
bai toan » bai tap
tang va » trang va, tang van, thang 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: theo tieu xanh - hanh tang va ((dung cong) OR (hang cong)) ((tap toan) OR (bai toan)) cau~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "theo tieu xanh - hanh tang va ((dung cong) or (hang cong)) ((tap toan) OR (bai toan)) cau~".
• Adding a wildcard symbol may retrieve word variants: theo tieu xanh - hanh tang va ((dung cong) or (hang cong)) ((tap toan) OR (bai toan)) cau*.