Perhaps you should try some spelling variations:
cach hoi » cach thoi, cach noi, cach hoc
hoc toan » hoc tan, hop toan, hoa toan
khoa hoc » hoa hoc
nhan dan » phan dau, nhan tai
gian dan » gian lang
su cach » su sach, tu cach, su cac
cuu mot » cua mot, cuu mo, huu mot
mot hoc » mon hoc, mo hoc, mot goc
hoi van » hoi va, hoi dan, hai van
ma hoi » mai hoi, xa hoi, ma hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: su cach hoi dap, nghien cuu mot hoc toan khoa hoc ma hoi van ((nhan dan) OR (gian dan))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su cach hoi dap, nghien cuu mot hoc toan khoa hoc ma hoi van ((nhan dan) OR (gian dan))".
• Adding a wildcard symbol may retrieve word variants: su cach hoi dap, nghien cuu mot hoc toan khoa hoc ma hoi van ((nhan dan) OR (gian dan))*.