Perhaps you should try some spelling variations:
mach tinh » mach tich, manh tinh, trach tinh
toan giao » ton giao, toan cao, hoa giao
kon mach » ke mach, ban mach
tinh son » tinh toan, dinh so, tinh hoc
bac dinh » xac dinh, bac ninh, ba dinh
don gian » dan gian
dinh su » dinh so, hinh su, dinh cu
vu bac » vu bach, vu ban, xu bac

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( kon mach tinh son - toan giao ) or ( vu bac dinh su - don gian ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( kon mach tinh son - toan giao ) OR ( vu bac dinh su - don gian )).
• Adding a wildcard symbol may retrieve word variants: (( kon mach tinh son - toan giao ) or ( vu bac dinh su - don gian ))*.