Perhaps you should try some spelling variations:
cam thuc » am thuc, nam thuc, cam thu
ty hang » ly hang, thi hang, thu hang
hieu ve » hieu va, hieu van
thuc ca » thuc cua, thuc can, thuc cao
vai cau » van cau, vai cac, lai chau
su sach » so sach, vu sach
ve cam » ve cham, ve cac, va cam
ca dan » cac dan, ca dao
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 ((ty hang) or (ty xang)) xa hoi. hieu ve cam thuc ca dan ((vai cau) OR (va cau)) treo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((ty hang) OR (ty xang)) xa hoi. hieu ve cam thuc ca dan ((vai cau) OR (va cau)) treo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ((ty hang) or (ty xang)) xa hoi. hieu ve cam thuc ca dan ((vai cau) OR (va cau)) treo".
• Adding a wildcard symbol may retrieve word variants: su sach ((ty hang) or (ty xang)) xa hoi. hieu ve cam thuc ca dan ((vai cau) OR (va cau)) treo*.