Perhaps you should try some spelling variations:
phap thong » phap phong, phap chong, pho thong
phu thong » pho thong, khau thong, phan thong
giai khoa » giao khoa, ngoai khoa, giai thoai
sach bai » sach dao, cac bai, sach xa
tac giai » tac gia, cac giai, tap giai
vu sach » vu bach, su sach, vu khach
bai tac » bai tap, bai toan, bai tang

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu sach bai tac giai khoa ((phu thong) or (phap thong))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach bai tac giai khoa ((phu thong) OR (phap thong)).
• Adding a wildcard symbol may retrieve word variants: vu sach bai tac giai khoa ((phu thong) or (phap thong))*.