Perhaps you should try some spelling variations:
cac thuc » cach thuc, can thuc, cay thuc
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
cac thu » cach thuc, cac thoi
thi cuu » thi cuc, thi huu, thi cu
cuu tre » cua tre, cau tren, cau treo
va cau » van cau, va cac, va dau

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 ky ((nang x) or (nang ma)) hoi. lieu va ((cac thuc) OR (cac thu)) va cau thi cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky ((nang x) OR (nang ma)) hoi. lieu va ((cac thuc) OR (cac thu)) va cau thi cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky ((nang x) or (nang ma)) hoi. lieu va ((cac thuc) OR (cac thu)) va cau thi cuu tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky ((nang x) or (nang ma)) hoi. lieu va ((cac thuc) OR (cac thu)) va cau thi cuu tre*.