Perhaps you should try some spelling variations:
sach van » sach han, sach va, bach van
van nang » van quang, van ban, van dong
van hanh » van thanh, ban hanh, van anh
cau thuc » cuu thuc, can thuc, cau phuc
su sach » so sach, vu sach
hanh de » hanh ve, hanh kem
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
de cua » le cua, te cua, dieu cua
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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 van nang ((x hoi) OR (o hoi)). hieu ve ((cau thuc) or (cau truc)) van hanh de cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach van nang ((x hoi) OR (o hoi)). hieu ve ((cau thuc) OR (cau truc)) van hanh de cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach van nang ((x hoi) OR (o hoi)). hieu ve ((cau thuc) or (cau truc)) van hanh de cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach van nang ((x hoi) OR (o hoi)). hieu ve ((cau thuc) or (cau truc)) van hanh de cua tre*.