Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
lang van » tang van, hoang van, giang van
dang van » hoang van, hang va
sach tay » xach tay, sach hay, sach nay
cam thuc » am thuc, nam thuc, cam thu
thuc van » thuc vat, thuc dan, thuc va
van hoan » van hoang, van hoa, van toan
hoan thi » hoang thi, doan thi, hoa thi
cua tre » cuu tre, cua triet, dua tren
hieu ve » hieu va, hieu van
ve cam » ve cham, ve cac, va cam
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach tay ((lang van) or (dang van)) hoi. hieu ve cam thuc van hoan thi ((cua tre) OR (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach tay ((lang van) OR (dang van)) hoi. hieu ve cam thuc van hoan thi ((cua tre) OR (cua te)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach tay ((lang van) or (dang van)) hoi. hieu ve cam thuc van hoan thi ((cua tre) OR (cua te))".
• Adding a wildcard symbol may retrieve word variants: toc sach tay ((lang van) or (dang van)) hoi. hieu ve cam thuc van hoan thi ((cua tre) OR (cua te))*.