Perhaps you should try some spelling variations:
cam thuc » am thuc, nam thuc, can thuc
hanh dao » lanh dao, thanh dat, thanh dam
van hanh » van thanh, ban hanh, van anh
hoang xa » hoang ha, hoang va, hoang xuan
sach thi » sach thu, sach tai, sach thieu
tu sach » thu sach, su sach, te sach
cam thu » nam thu, cac thu, ca thu
so viet » hoc viet
hieu ve » hieu va, hieu van
hang xa » hang va, hang ca, lang xa
dao so » dai so, dao o, dao do

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach thi ((hang xa) or (hoang xa)) hoi. hieu ve ((cam thuc) or (cam thu)) van hanh dao so viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thi ((hang xa) OR (hoang xa)) hoi. hieu ve ((cam thuc) OR (cam thu)) van hanh dao so viet.
• Adding a wildcard symbol may retrieve word variants: tu sach thi ((hang xa) or (hoang xa)) hoi. hieu ve ((cam thuc) or (cam thu)) van hanh dao so viet*.