Perhaps you should try some spelling variations:
hieu toan » bieu toan, thien toan, kiem toan
vat thanh » dat thanh, gat thanh, tat thanh
toan cau » toan cao, toan ban, toan tap
cau tren » dau tren, ca tren, cau treo
thanh va » thanh van, hanh va, thanh ha
cau thuc » cau truc, cuu thuc, can thuc
su sach » so sach, vu sach
ky tang » ky nang, ky dang, kho tang
ky lang » ky nang, ky dang, tay lang
cu tren » tu tren, dua tren

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 lang) OR (ky tang)) xa hoi. hieu toan cau thuc vat thanh va ((cau tren) or (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((ky lang) OR (ky tang)) xa hoi. hieu toan cau thuc vat thanh va ((cau tren) OR (cu tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ((ky lang) OR (ky tang)) xa hoi. hieu toan cau thuc vat thanh va ((cau tren) or (cu tren))".
• Adding a wildcard symbol may retrieve word variants: su sach ((ky lang) OR (ky tang)) xa hoi. hieu toan cau thuc vat thanh va ((cau tren) or (cu tren))*.