Perhaps you should try some spelling variations:
hieu toan » bieu toan, thien toan, kiem toan
gat thanh » dat thanh, tat thanh, vat thanh
toan cau » toan cao, toan ban, toan tap
cau thuc » cau truc, cuu thuc, can thuc
thuc gat » thuc vat, thuc giai, thuc hoat
thanh va » thanh van, hanh va, thanh ha
cau tren » dau tren, ca tren, cau treo
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
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 xa hoi. hieu toan cau thuc gat thanh va ((cau tren) or (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky lang xa hoi. hieu toan cau thuc gat thanh va ((cau tren) OR (cu tren)).
• Adding a wildcard symbol may retrieve word variants: su sach ky lang xa hoi. hieu toan cau thuc gat thanh va ((cau tren) or (cu tren))*.