Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cuu thuc » cuu tac
cau thuc » cau truc, can thuc, cau phuc
tu sach » thu sach, su sach, te sach
hanh ha » nhanh ha, thanh ha, hanh hoa
va hanh » van hanh, va thanh, va danh
hieu va » lieu va, hieu qua
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
ha cua » hoa cua, hai cua, nha cua

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) or (toc sach)) ky tang ma hoi. hieu va ((cau thuc) or (cuu thuc)) va hanh ha cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky tang ma hoi. hieu va ((cau thuc) OR (cuu thuc)) va hanh ha cua tre.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky tang ma hoi. hieu va ((cau thuc) or (cuu thuc)) va hanh ha cua tre*.