Perhaps you should try some spelling variations:
hieu toan » bieu toan, thien toan, kiem toan
toan cau » toan cao, toan ban, toan tap
cau thuc » cau truc, cuu thuc, can thuc
vat hanh » vat thanh, van hanh, nhat hanh
su sach » so sach, vu sach
va hanh » van hanh, va thanh, va danh
ca tren » cau tren, la tren, co tren
cu tren » tu tren, dua tren
sach ky » sac ky, sach y, sach ty
tang xa » trang xa, tang ma, lang xa
ky tang » ky nang, ky dang, kho tang

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