Perhaps you should try some spelling variations:
thanh trung » thanh tung
hieu xanh » chieu xanh, hieu manh, hieu nganh
trung can » trung cap, trung van, trong can
dung cong » dung trong
doc hieu » toc thieu, hoc thieu, hoc hien
can dung » chan dung, van dung, dan dung
tan toan » tan tran, tap toan, van toan
bai toan » bai tap

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc hieu xanh - thanh trung can dung cong ((tan toan) or (bai toan)) cau~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu xanh - thanh trung can dung cong ((tan toan) OR (bai toan)) cau.
• Adding a wildcard symbol may retrieve word variants: doc hieu xanh - thanh trung can dung cong ((tan toan) or (bai toan)) cau*.