Perhaps you should try some spelling variations:
phuong cong » phuong dong, phong cong, phung cong
theo chieu » theo tieu, theo chu, thi chieu
hanh tang » hanh trang, anh tang, hanh mang
va phuong » va thuong, cac phuong
ho chieu » hoc thieu, doi chieu, mot chieu
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.

• Performing a fuzzy search may retrieve terms with similar spellings: ((theo chieu) or (ho chieu)) xanh - hanh tang va phuong cong ((tap toan) OR (bai toan)) cau~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((theo chieu) OR (ho chieu)) xanh - hanh tang va phuong cong ((tap toan) OR (bai toan)) cau.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((theo chieu) or (ho chieu)) xanh - hanh tang va phuong cong ((tap toan) OR (bai toan)) cau".
• Adding a wildcard symbol may retrieve word variants: ((theo chieu) or (ho chieu)) xanh - hanh tang va phuong cong ((tap toan) OR (bai toan)) cau*.