Perhaps you should try some spelling variations:
hieu toan » bieu toan, thien toan, kiem toan
toan cau » toan cao, toan ban, toan tap
cau treo » cau theo, cau tren, cau triet
vat hanh » vat thanh, van hanh, va hanh
cau thuc » cau truc, cuu thuc, can thuc
hanh va » hang va, hanh vi
cu tren » tu tren, dua tren
lang xa » lang ha, dang xay, lang van
sac ky » cac ky

You may be able to get more results by adjusting your search query.

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