Perhaps you should try some spelling variations:
hieu toan » bieu toan, thien toan, kiem toan
toan tap » toan ban
tap thuc » tap tuc, tam thuc, toan thuc
vat hanh » vat thanh, van hanh, va hanh
cau tren » dau tren, ca tren, cau treo
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
ky tang » ky nang, ky dang, kho tang
tang xa » trang xa, tang ma, lang xa
hanh va » hang va, hanh vi
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 tang xa hoi. hieu toan tap thuc vat hanh va ((cau 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 tap thuc vat hanh va ((cau tren) OR (cu tren)).
• Adding a wildcard symbol may retrieve word variants: su sach ky tang xa hoi. hieu toan tap thuc vat hanh va ((cau tren) or (cu tren))*.