Perhaps you should try some spelling variations:
doi chieu » doc hieu, doi chi, ho chieu
mot chieu » ho chieu
trong bai » trong ban, thong bai, trong hai
cua rang » cua hang, cua lang, cua mang
cua dang » cua cong, cua ban
bai toan » bai tap
toan cao » toan ban, toan tap

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: ((doi chieu) OR (mot chieu)) sach - canh tranh ((cua rang) OR (cua dang)) trong bai toan cao~.
• Adding a wildcard symbol may retrieve word variants: ((doi chieu) or (mot chieu)) sach - canh tranh ((cua rang) or (cua dang)) trong bai toan cao*.