Perhaps you should try some spelling variations:
doanh hai » doanh tai, doan hai, doanh ha
thuc luat » thue luat, thuc luan, thuoc luan
cau tren » cu tren, dau tren, ca tren
cam thuc » am thuc, nam thuc, cam thu
hieu van » hieu va, thien van, lieu va
hai cau » hai chau, hai chu, hai hau
van cam » van nam, van lam, van cau
su sach » so sach
nang ma » sang ma, nang cao, mang may
vu sach » vu bach, vu khach
tang ma » mang may, tang van

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((su sach) or (vu sach)) ly ((nang ma) OR (tang ma)) hoi. hieu van cam thuc luat doanh hai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (vu sach)) ly ((nang ma) OR (tang ma)) hoi. hieu van cam thuc luat doanh hai cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (vu sach)) ly ((nang ma) OR (tang ma)) hoi. hieu van cam thuc luat doanh hai cau tren".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (vu sach)) ly ((nang ma) OR (tang ma)) hoi. hieu van cam thuc luat doanh hai cau tren*.